Change Python version in setup step to 3.9

Author: molinav

.github/workflows/build.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v4
         with:
-          python-version: "3.8"
+          python-version: "3.9"
 
       - name: Install build dependencies
         run: |