How do I resolve the GitHub internal server error?

The GitHub internal server error you are facing seems related to the security issue reported on https://github.blog/2022-04-15-security-alert-stolen-oauth-user-tokens/

And based on this ongoing incident, As reported yesterday, revocation of all OAuth tokens from the Heroku Dashboard GitHub integration is complete. Until further notice, we will not issue OAuth tokens from the Heroku Dashboard. These actions, based on our current understanding of the issue, should prevent unauthorized access to your GitHub repositories.

We will continue to work with GitHub to provide additional guidance on how to review your GitHub logs for evidence of exfiltration or malicious activity. Please reach out to security@salesforce.com with any information that may assist us with our ongoing investigation. Please continue to visit status.heroku.com for the latest updates.