updated actions to fix deprecation warnings

.github/workflows/python-tests.yml

@@ -18,9 +18,9 @@ jobs:
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@main
     - name: Set up Python ${{ matrix.python }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@main
       with:
         python-version: ${{ matrix.python }}
     - name: Install dependencies