CI: Remove test without loader from unit-tests for domain linkage

[Sandra Vrtikapa]

This test is trying to access remote URL and it is failing too often.

--- FAIL: TestParseLinkedData/success_-default_options (0.29s)
didconfig_test.go:58:
Error Trace: /Users/runner/work/aries-framework-go/aries-framework-go/pkg/doc/didconfig/didconfig_test.go:58
Error: Received unexpected error:
domain linkage credential(s) not found
Test: TestParseLinkedData/success-_default_options