SSOSync fails to get binary secrets

[Dan Corne]

Describe the bug
If any of the secrets for the Lambda are stored as binary rather than strings, SSOSync stops working with the following error:

{"level":"fatal","msg":"cannot read config: illegal base64 data at input byte 0","time":"2023-05-02T08:04:04Z"} 

To Reproduce
Update one of the secrets to use binary rather than string, eg with the command:

aws secretsmanager update-secret --secret-id SSOSyncGoogleCredentials --secret-binary $(cat credentials.json | base64)

Expected behavior
SSOSync fetches the secret and continues to run.