bug(ci): commit message validation checks the wrong object under pull_request

[Sober7135]

Describe the bug, including details regarding any error messages, version, and platform.

Repository policy

CONTRIBUTING.md states that all pull requests are squash merged.

However, #876 adds a CI check that validates the wrong object under the pull_request event.

Current behavior

#876 validates the merge-ref commit message

incubator-graphar/.github/workflows/ci.yml

Lines 105 to 109 in d535a43

	- name: Validate commit message format
	run: |
	COMMIT_MSG=$(git log -1 --pretty=%B)
	echo "$COMMIT_MSG" > .git/COMMIT_EDITMSG
	pre-commit run --hook-stage commit-msg --commit-msg-filename .git/COMMIT_EDITMSG

Under pull_request, actions/checkout checks out the PR merge ref by default, not the PR head commit.

A temporary reproduction in PR #892 , action see https://github.com/apache/incubator-graphar/actions/runs/22542566764/job/65299867120?pr=892
In this action, I added cat .git/COMMIT_EDITMSG,

    - name: Validate commit message format
      run: |
        COMMIT_MSG=$(git log -1 --pretty=%B)
        echo "$COMMIT_MSG" > .git/COMMIT_EDITMSG
        cat .git/COMMIT_EDITMSG
        pre-commit run --hook-stage commit-msg --commit-msg-filename .git/COMMIT_EDITMSG 

the output is

Merge 8255be0ba41d4142ecaae5296aaa79c25f3e639a into d535a437667c6e2bf28f7f376930b13ed5aed63d

And see also:

• actions/checkout 's docs: https://github.com/actions/checkout?tab=readme-ov-file#checkout-pull-request-head-commit-instead-of-merge-commit
• stackoverflow discussion: https://stackoverflow.com/questions/62334460/git-history-in-a-github-action

Expected behavior

Under squash merge, the meaningful metadata for what lands in main is the PR title / final squash commit message.

And I think we should add this CI for all PRs not just C++ PR

Component(s)

Developer Tools

[SYaoJun]

I’m so sorry for introducing these bugs.