Skip CLA check for bot accounts

[aconite33]

Summary

Fixes CLA check failures on automated PRs from bot accounts (e.g. dependabot, renovate).

The existing allowlist field in the CLA assistant action was not matching bot authors correctly, causing PRs like #3009 to fail the CLA check. This adds an explicit bot detection step that:

1. Checks if the PR author's login ends with [bot]
2. Sets a success commit status for CLAAssistant when a bot is detected
3. Skips the CLA assistant action entirely via an additional if condition

This is in addition to the existing org membership skip and the CLA assistant's own allowlist, providing a reliable fallback.

Test plan

• Merge this PR, then re-run the CLA check on Bump pyjwt from 2.11.0 to 2.12.0 #3009 (dependabot PR) and verify it passes
• Verify normal CLA flow still works for non-bot, non-member PRs
• Once validated here, roll out to other org repos

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92%. Comparing base (593fe04) to head (802603c).

Additional details and impacted files

@@          Coverage Diff           @@
##           stable   #3010   +/-   ##
======================================
- Coverage      92%     92%   -0%     
======================================
  Files         416     416           
  Lines       34690   34690           
======================================
- Hits        31645   31641    -4     
- Misses       3045    3049    +4     

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