Run PR check action on synchronize

[dmjb]

When reusing this action elsewhere, I noticed that its status would be cleared if additional commits were pushed to the PR branch. Triggering on the synchronize event ensures that it will be checked on subsequent commits.

Summary

Provide a brief overview of the changes and the issue being addressed.
Explain the rationale and any background necessary for understanding the changes.
List dependencies required by this change, if any.

Fixes #(related issue)

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Outline how the changes were tested, including steps to reproduce and any relevant configurations.
Attach screenshots if helpful.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 55.187% (-0.007%) from 55.194%
when pulling f98ceaa on fix-pr-check-action
into c2d9126 on main.