test: install ffmpeg for pytests (#3499)

.github/workflows/api-tests.yml

@@ -32,6 +32,11 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install APT packages
+        uses: awalsh128/cache-apt-pkgs-action@v1
+        with:
+          packages: ffmpeg
+
       - name: Set up Python
         uses: actions/setup-python@v5
         with: