Description of the problem:
The GitHub Sign In card is always shown regardless of the auth configuration in backstage, giving the impression to the user that it is possible to login to GitHub as an alternative method. However, when clicking the link, a popup is opened with a JSON error:

{"error":{"name":"NotFoundError","message":"No auth provider registered for 'github'"},"request":{"method":"GET","url":"/api/auth/github/start?scope=read%3Auser&origin=https%3A%2F%2Fbackstage-backstage-rhdh-operator.apps.stress.parodos.dev&flow=popup&env=development"},"response":{"statusCode":404}} 

**

How reproducible:

All the time.

Steps to reproduce:

1. Configure RHDH without providing GITHUB_TOKEN and GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET values in the secret.
2. Restart the backstage pod and wait for it to reach Ready status.
3. Open a browser and load the landing page.
4. Click on the Sign in using GitHub button.

Actual results:

Shows a popup window with a json that has a 404 HTTP status

Expected results:

Either the landing page should not show the GitHub card for signing in or it should open a popup window with a GitHub authentication page (login/password) that, once populated and validated by GitHub, should close and authenticate the user in Backstage.