Support merge queue

[masaru-iritani]

I'll publish this pull request once confirmed it's good to go by maintainers.

What

This pull request adds a support for merge_group event.

Why

Closes #183
Closes #253

Some repositories (including my organization's one) enable the merge queue, where pull requests are queued to be checked sequentially. It's common (I believe) to use the same test workflow for both pull_request event and merge_group event, which is triggered when a change gets into or out of the merge queue.

Currently, paths-filter action doesn't do anything special for detecting the base commit for a commit in the merge queue. Therefore, if the merge queue has multiple pull requests, the diff may include changes from other pull requests and cause false-positives.

Specifying the base and ref explicitly from the merge_group event (as shown in #183) can workaround the problem. But it'd be great if paths-filter can handle them by default.

This change won't break existing workflows already specifying ref and base explicitly because manual inputs take precedence over commit hashes from the event (unlike pull_request events where manual inputs are ignored).

[efenderbosch-atg]

In the meantime, we are trying this setup for merge queues:

      - name: Find Changes
        uses: dorny/paths-filter@v3
        id: find_changes
        with:
          # For merge group events, compare against the target branch (main)
          base: ${{ github.event_name == 'merge_group' && github.event.merge_group.base_ref || '' }}
          # For merge group events, use the merge group head ref
          ref: ${{ github.event_name == 'merge_group' && github.event.merge_group.head_sha || github.ref }}

[saschabratton]

@masaru-iritani lgtm. We should add this. Do you want to commit the build?

[masaru-iritani]

@saschabratton Thank you for taking a look! I realized my previous suggestion to match the type of pull request-related events wasn’t quite right. I pushed another commit that corrects it by keeping the existing behavior and updating the type annotation. If it looks good to you, I’d appreciate it if you could merge this pull request.

[saschabratton]

@masaru-iritani I think it's fine either way. It's only referencing .number which is the same on both. But yes, correcting the type being cast instead of the assignment works just as well.

You just need to build the dist and we can merge this 👍🏻

[masaru-iritani]

@saschabratton I executed npm run pack and pushed a commit with the diff. Please let me know if I should have done anything differently.