[CI] Upgrade to actions/checkout@v4

To silence this warning in the GitHub CI logs:

    The following actions use a deprecated Node.js version and will be
    forced to run on node20: actions/checkout@v3. For more info:
    https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

.github/workflows/build-and-run-tests.yml

@@ -23,9 +23,9 @@ jobs:
       PREFIX: ${{ github.workspace }}/_local
     steps:
       # Check out project
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       # Check out dependencies
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           repository: google/googletest
           ref: 8d51dc50eb7e7698427fed81b85edad0e032112e