Adding upstream version 20.3.0.

Signed-off-by: Daniel Baumann <daniel@debian.org>

.github/workflows/python-package.yml

@@ -17,9 +17,15 @@ jobs:
       uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
+    - name: Create a virtual environment
+      run: |
+        python -m venv .venv
     - name: Install dependencies
       run: |
+        source ./.venv/bin/activate
         python -m pip install --upgrade pip
         make install-dev
     - name: Run checks (linter, code style, tests)
-      run: make check
+      run: |
+        source ./.venv/bin/activate
+        make check