ci: pip install pytest-mock

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install flake8 pytest
+          pip install flake8 pytest pytest-mock
           pip install --use-pep517 -r requirements.txt
       - name: Lint with flake8
         run: |