fix: Ensure JS Test Summary always reports status (#11645)
## Summary
- Move path filtering from workflow-level trigger to job-level
conditions
- Ensures the summary job always runs and posts a status to GitHub
When path filters are at the workflow level and paths don't match, the
workflow never runs, so required status checks never receive a status
and hang indefinitely as "Waiting for status to be reported."
By moving the filtering inside the workflow, the `find-changes` job
always runs and the summary job can report success/skip appropriately.
## Testing
This PR itself will validate the fix - the "JS Test Summary" check
should complete (likely with a skip message since no JS packages are
modified).
