fixing (some) github actions warnings

Author: wolph

.github/workflows/main.yml

@@ -14,9 +14,9 @@ jobs:
         python-version: ['3.7', '3.8', '3.9', '3.10']
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies