Use system python3

.github/workflows/test.yml

@@ -32,14 +32,10 @@ jobs:
     if: github.event_name == 'push' && github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
     steps:
-      - name: Set up Python
-        uses: actions/setup-python@v1
-        with:
-          python-version: 3.x
       - name: Install Coveralls
-        run: python -m pip install coveralls
+        run: python3 -m pip install coveralls
       - name: Call Coveralls parallel builds webhook
-        shell: python
+        shell: python3 {0}
         env:
           COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}
         run: |