ci: update action versions

Author: vsergeev

.github/workflows/tests.yml

@@ -24,7 +24,7 @@ jobs:
     container: ${{ matrix.container }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Set up Python ${{ matrix.python-version }}
       if: ${{ matrix.python-version != '2.7' }}