oasdiff diff result fails to detect changes with --flatten flag

[Bianca Lisle]

Describe the bug
oasdiff diff result fails to detect changes with --flatten flag
To Reproduce
Steps to reproduce the behavior:

1. The command-line,

 ❯ oasdiff diff --flatten  data/spec1_chained_diff.yaml data/spec2_chained_diff.yaml --max-circular-dep 10  --strip-prefix-base /api/atlas/v1.0 --strip-prefix-revision /api/atlas/v2 --match-path "^.+\/(v1.0|v2)\/.+$"

2. Spec 1
3. Spec 2
4. Output

paths:
    modified:
        /subscribe:
            operations:
                modified:
                    GET:
                        responses:
                            modified:
                                "200":
                                    content:
                                        mediaTypeModified:
                                            application/json:
                                                schema:
                                                    items:
                                                        oneOf:
                                                            modified:
                                                                '#/components/schemas/FederationOidcIdentityProvider':
                                                                    oneOf:
                                                                        modified:
                                                                            '#/components/schemas/FederationSamlIdentityProvider':
                                                                                oneOf:
                                                                                    added:
                                                                                        - FederationSamlIdentityProvider
                                                                                        - FederationOidcIdentityProvider
                                                                '#/components/schemas/FederationSamlIdentityProvider':
                                                                    oneOf:
                                                                        added:
                                                                            - FederationSamlIdentityProvider
                                                                            - FederationOidcIdentityProvider
endpoints:
    modified:
        ?   method: GET
            path: /subscribe
        :   responses:
                modified:
                    "200":
                        content:
                            mediaTypeModified:
                                application/json:
                                    schema:
                                        items:
                                            oneOf:
                                                modified:
                                                    '#/components/schemas/FederationOidcIdentityProvider':
                                                        oneOf:
                                                            modified:
                                                                '#/components/schemas/FederationSamlIdentityProvider':
                                                                    oneOf:
                                                                        added:
                                                                            - FederationSamlIdentityProvider
                                                                            - FederationOidcIdentityProvider
                                                    '#/components/schemas/FederationSamlIdentityProvider':
                                                        oneOf:
                                                            added:
                                                                - FederationSamlIdentityProvider
                                                                - FederationOidcIdentityProvider
components:
    schemas:
        modified:
            FederationIdentityProvider:
                oneOf:
                    modified:
                        '#/components/schemas/FederationOidcIdentityProvider':
                            oneOf:
                                modified:
                                    '#/components/schemas/FederationSamlIdentityProvider':
                                        oneOf:
                                            added:
                                                - FederationSamlIdentityProvider
                                                - FederationOidcIdentityProvider
                        '#/components/schemas/FederationSamlIdentityProvider':
                            oneOf:
                                added:
                                    - FederationSamlIdentityProvider
                                    - FederationOidcIdentityProvider
            FederationOidcIdentityProvider:
                oneOf:
                    modified:
                        '#/components/schemas/FederationOidcIdentityProvider':
                            oneOf:
                                modified:
                                    '#/components/schemas/FederationSamlIdentityProvider':
                                        oneOf:
                                            added:
                                                - FederationSamlIdentityProvider
                                                - FederationOidcIdentityProvider
                        '#/components/schemas/FederationSamlIdentityProvider':
                            oneOf:
                                added:
                                    - FederationSamlIdentityProvider
                                    - FederationOidcIdentityProvider
            FederationSamlIdentityProvider:
                oneOf:
                    added:
                        - FederationSamlIdentityProvider
                        - FederationOidcIdentityProvider

Expected behavior
No changes.
Desktop (please complete the following information):

• OS: [e.g. iOS]

Additional context
Add any other context about the problem here.

[Reuven Harrison]

Fixed by #466