Fix assertions in OAuth clients test
We had test that started to be flakey recently:
oauth-client-api
GET /v1/oauth-clients returns list of OAuth clients the user owns
Failed builds:
- https://gitlab.com/gitlab-org/gitter/webapp/-/jobs/529520773
- https://gitlab.com/gitlab-org/gitter/webapp/-/jobs/528038735
Fix
Compare result with two OAuth clients instead of one.