Install ffmpeg also

Author: pgleeson

.github/workflows/build.yml

@@ -25,9 +25,10 @@ jobs:
         python-version:  ${{ matrix.python-version }}
 
 
-    - name: Install Python dependencies
+    - name: Install dependencies
       run: |
-
+       sudo apt-get update
+        sudo apt-get install ffmpeg -y 
         pip install numpy matplotlib ruff 
 
     - name: Test WCONViewer