Sumatra needs to be installed to run tests

.github/workflows/tests.yml

@@ -23,11 +23,12 @@ jobs:
         uses: actions/setup-python@v3
         with:
           python-version: ${{ matrix.python-version }}
-      - name: Install dependencies
+      - name: Install
         run: |
           python -m pip install --upgrade pip
           pip install -r ci/requirements.txt
           pip install -r ci/requirements-test.txt
+          pip install .
       - name: Lint with flake8
         run: |
           # stop the build if there are Python syntax errors or undefined names