Fetch more in actions/checkout for finding changed files (#51392)

.github/workflows/codeowners-legal.yml

@@ -30,6 +30,12 @@ jobs:
     steps:
       - name: Check out repo
         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
 
       - name: Get changed files
         id: changed-files