[executorch] Make trymerge force merges actually work with executorch (#121920)
This PR addresses an issue with the trymerge function for executorch, which currently uses Facebook CLA instead of Easy CLA. This bug has been patched in #121921. However, the patch is potentially controversial, and we still want to verify Facebook CLA if it exists. Therefore, this PR includes Facebook CLA in our set of mandatory checks.
Additionally, this PR removes Facebook CLA from one of the mocks. This change is necessary because the specific PR used for testing fails due to the presence of Facebook CLA in the mock.
## Testing:
We run `find_matching_merge_rule(pr = GitHubPR("pytorch", "executorch", 2326), skip_mandatory_checks=True, skip_internal_checks=True)` to check if things work
https://pastebin.com/HHSFp2Gw
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121920
Approved by: https://github.com/huydhn
