Run changed-files before cloning github/github (#49916)

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

@@ -34,6 +34,12 @@ jobs:
     steps:
       - name: Check out repo's default branch
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+        with:
+          # Picking this number is a "best guess". If we make it too large,
+          # the checkout will take potentially unnecessariily long.
+          # This reduces the chance that tj-actions/changed-files has to
+          # fetch deeper history. But if it needs to, it will.
+          fetch-depth: 10
 
       - uses: ./.github/actions/node-npm-setup
 
@@ -100,6 +106,7 @@ jobs:
       # workaround for the time being.
       # First, gather the URLs that were relevant
       - name: Get changed content/data files
+        if: ${{ github.event_name == 'pull_request' }}
         id: changed-files
         uses: tj-actions/changed-files@77af4bed286740ef1a6387dc4e4e4dec39f96054 # v43.0.0
         with:
@@ -109,6 +116,7 @@ jobs:
           safe_output: false
           files: |
             content/**
+
       - name: Generate PR comment
         if: ${{ github.event_name == 'pull_request' && steps.changed-files.outputs.any_changed == 'true' }}
         env: