Handle GitHub App token revocation connection errors

[cursor]

Summary

• Prevents ConnectionError during GitHub App token revocation from failing webhook processing.
• Treats token revocation as best-effort cleanup in GithubAppToken.get_token().
• Adds regression tests for revocation network failures and token-creation failures.

Root Cause

GithubAppToken.get_token() performed requests.delete() in a finally block without exception handling. When GitHub closed the connection during token revocation (RemoteDisconnected/ConnectionError), that cleanup exception escaped and bubbled up to the Flask handler, producing 500s and Sentry errors even when the main webhook handling path had succeeded.

Changes

• Updated src/github_app.py:
  • Added module logger.
  • Wrapped revocation requests.delete() in try/except requests.RequestException.
  • Logs warning with context (installation_id) and traceback instead of raising.
• Added tests/test_github_app.py:
  • Verifies revocation connection errors are ignored and only logged.
  • Verifies access-token creation errors still raise and no revocation attempt is made.

Validation

• python3 -m pytest tests/test_github_app.py tests/test_web_app_handler.py
• Result: 10 passed, 1 skipped.