GitHub App auth provider: Pass validation when configuring users and groups

[rak-phillip]

Summary

This allows the GitHub/GitHub App auth providers to pass validation when configuring users and groups.

Fixes #15648

Occurred changes and/or fixed issues

• Pass validation when configuring users and groups

Technical notes summary

The github app auth provider was preventing admins from configuring users and groups because validation will fail without a client secret. Other auth providers, like shell/edit/auth/oidc.vue, get around this by short-circuiting to true when not editing the config.

Areas or cases that should be tested

• GitHub auth provider
• GitHub App auth provider

Areas which could experience regressions

NA

Screenshot/Video

NA

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
• The PR has been reviewed in terms of Accessibility
• The PR has considered, and if applicable tested with, the three Global Roles Admin, Standard User and User Base

[eva-vashkevich]

lgtm