Update GitHub Actions config to install SDL_Mixer

Author: benstone

.github/workflows/build.yml

@@ -159,7 +159,7 @@ jobs:
       - name: Install Packages
         run: |
           sudo apt-get update &&
-          sudo apt-get install -y g++ cmake libsdl2-dev libsdl2-ttf-dev libgtk-3-dev zenity ninja-build
+          sudo apt-get install -y g++ cmake libsdl2-dev libsdl2-ttf-dev libsdl2-mixer-dev libgtk-3-dev zenity ninja-build
       - name: Check out repository code
         uses: actions/checkout@v4
       - name: CMake Generate