On PRs only check URLs in github/github that are relevant (#49902)

.github/workflows/validate-github-github-docs-urls.yml

@@ -8,7 +8,15 @@ on:
   workflow_dispatch:
   schedule:
     - cron: '20 16 * * *' # Run every day at 16:20 UTC / 8:20 PST
-  # pull_request: # Temporarily commented out. See internal issue 4152
+  pull_request:
+    paths:
+      - 'content/**'
+      # In case a relevant dependency changes
+      - 'package*.json'
+      # The scripts
+      - 'src/links/scripts/validate-github-github-docs-urls/**'
+      # The workflow
+      - .github/workflows/validate-github-github-docs-urls.yml
 
 permissions:
   contents: read
@@ -90,13 +98,28 @@ jobs:
       # In the latter case, you might want to update the URL in docs-urls.json
       # after this PR has landed, or consider using `<a name="..."></a>` as a
       # workaround for the time being.
+      # First, gather the URLs that were relevant
+      - name: Get changed content/data files
+        id: changed-files
+        uses: tj-actions/changed-files@77af4bed286740ef1a6387dc4e4e4dec39f96054 # v43.0.0
+        with:
+          # No need to escape the file names because we make the output of
+          # tj-actions/changed-files be set as an environment variable. Not
+          # as a direct input to the line of bash that uses it.
+          safe_output: false
+          files: |
+            content/**
       - name: Generate PR comment
-        if: ${{ github.event_name == 'pull_request' }}
+        if: ${{ github.event_name == 'pull_request' && steps.changed-files.outputs.any_changed == 'true' }}
         env:
+          # Make it an environment variable so that its value doesn't need to be escaped.
+          # See https://docs.github.com/en/actions/security-guides/security-hardening-for-github-actions#using-an-intermediate-environment-variable
+          CHANGED_FILES: |-
+            ${{ steps.changed-files.outputs.all_changed_files }}
           GITHUB_TOKEN: ${{ secrets.DOCS_BOT_PAT_WRITEORG_PROJECT }}
           ISSUE_NUMBER: ${{ github.event.pull_request.number }}
           REPOSITORY: ${{ github.repository }}
-        run: npm run validate-github-github-docs-urls -- post-pr-comment checks.json
+        run: npm run validate-github-github-docs-urls -- post-pr-comment checks.json --changed-files $CHANGED_FILES
 
       - uses: ./.github/actions/slack-alert
         if: ${{ failure() && github.event_name == 'schedule' }}