CLI minder repo delete fails when access to github repository is revoked

[blkt]

Describe the issue

An admin can pick which repositories are accessible to Minder during and after enrollment via github.
When a repository originally accessible to Minder gets removed from the list of accessible repositories we loose access to its webhook and can't delete neither the webhook nor the repository from the DB, despite being effectively impossible to manage for Minder.

error deleting repository from DB: error deleting webhook: error deleting hook: DELETE https://api.github.com/repos/blkt/go-github/hooks/482253255: 403 Resource not accessible by integration []

Note that this might be exacerbated by auto-registration.

A sound behaviour must be defined and implemented for this scenario.

To Reproduce

First, enroll and register a repo

# grant access to all repositories during enrollment
$ minder provider enroll
$ minder repo register -n <repo>

Then, remove the repository from the list under "Repository access" in the installation's page.
Finally

$ minder repo delete -n <repo>

What version are you using?

v0.0.51

[evankanderson]

Did we fix this with #3447?