ci: trigger check-docs on changes to its own workflow file

The job's PR trigger only watched docs/** before, so workflow-only
changes (like the previous puppeteer fix in this PR) skipped the
check-docs run on the PR that introduced them. Add the workflow
file itself to the path filter so future workflow edits are
verified against link-check behavior before merge.

.github/workflows/weekly-docs.yaml

@@ -9,6 +9,7 @@ on:
       - main
     paths:
       - "docs/**"
+      - ".github/workflows/weekly-docs.yaml"
 
 permissions:
   contents: read