Upgrade github action

Author: gnthibault

.github/workflows/pythonapp.yml

@@ -19,11 +19,10 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
-    - name: Set up Python 3.8
-      uses: actions/setup-python@v1
+    - uses: actions/checkout@v3
+    - uses: actions/setup-python@v4
       with:
-        python-version: 3.8
+        python-version: '3.8'
     - name: Install dependencies
       run: |
         sudo apt-get install libgraphviz-dev