Update coverage.yml

Install ffmpeg for tests

.github/workflows/coverage.yml

@@ -25,6 +25,8 @@ jobs:
           python -m pip install --upgrade pip
           python -m pip install flake8 pytest
           python -m pip install -e .
+      - name: Setup FFmpeg
+        uses: FedericoCarboni/setup-ffmpeg@v2
       - name: Generate coverage report
         run: |
           pip install pytest