Add tests for `check_changes_for_autoapproval` and `check_authorized_users`

[dylanhmorris]

Definition of done:

• Test that confirms each function raises no error on valid changes to model-output
• Tests that confirm check_changes_for_autoapproval errors informatively when:
  • no changed files
  • changed files outside model-output
  • changes inside model-output by a user not authorized to change anything in model-output
  • changes inside model-output by a user not authorized to change some things in model-output but not what they actually changed

Other tests as appropriate.