GitHub Actions: Upgrade to actions/checkout@v4

https://github.com/actions/checkout/releases

Author: cclauss

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
       COVERAGE_OPTIONS: "-a"
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v4
         with: