fix(test): configure core.hooksPath for test_end_to_end_post_commit_runs

[google-labs-jules]

The test test_end_to_end_post_commit_runs was failing because the post-commit hook was not being executed in the temporary repository, likely due to a global git configuration overriding core.hooksPath (e.g., to /dev/null).

This change ensures that core.hooksPath is explicitly set to .git/hooks in the temporary test repository during initialization, allowing the local git hook to run as intended and the test to pass.

Also updated CHANGELOG.md under [Unreleased] with a summary of the fix. All tests, build checks, and docguard validation are now passing.

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PR created automatically by Jules for task 17418356542296495749 started by @raccioly

[google-labs-jules]

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