CI: Update first-party GitHub Actions from v2 to v4

GitHub Actions has deprecated Actions based on node16. The v4 actions
are based on node20. Replace first-party v2 actions with their v4
counterparts.

See:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

.github/workflows/clang-format.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           submodules: 'recursive'