Github: Support a timeout on checkout

Sometimes github or the CI runner times out trying to checkout the
source and stays timing out forever.

Give it a three minute timeout otherwise the CI runner will stall
forever.

.github/workflows/pr-code-format.yml

@@ -20,6 +20,7 @@ jobs:
 
       - name: Checkout through merge base
         uses: rmacklin/fetch-through-merge-base@v0
+        timeout-minutes: 3
         with:
           base_ref: ${{ github.event.pull_request.base.ref }}
           head_ref: ${{ github.event.pull_request.head.sha }}