Handle GitHub App token revoke timeouts without masking primary errors

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Summary

• guard GitHub App installation-token revocation in GithubAppToken.get_token() so cleanup network failures do not raise out of the context manager
• log revocation failures at warning level with traceback for observability
• add targeted unit tests for normal revocation flow and the regression case where cleanup timeout would mask the primary exception

Validation

• python3 -m pytest tests/test_github_app.py tests/test_web_app_handler.py -q

Context

• Investigates and mitigates Sentry issue SENTRY-GITHUB-ACTIONS-APP-6X (issue link) reporting ConnectTimeout against GitHub API during token cleanup.