Ensure mp3gain is installed in CI

.github/workflows/ci.yaml

@@ -35,7 +35,12 @@ jobs:
           python-version: ${{ matrix.python-version }}
           cache: poetry
 
-      - name: Install PyGobject and release script dependencies on Ubuntu
+      - name: Install system dependencies on Windows
+        if: matrix.platform == 'windows-latest'
+        run: |
+          choco install mp3gain -y
+
+      - name: Install system dependencies on Ubuntu
         if: matrix.platform == 'ubuntu-latest'
         run: |
           sudo apt update
@@ -43,11 +48,12 @@ jobs:
             ffmpeg \
             gobject-introspection \
             gstreamer1.0-plugins-base \
-            python3-gst-1.0 \
+            imagemagick \
             libcairo2-dev \
             libgirepository-2.0-dev \
+            mp3gain \
             pandoc \
-            imagemagick
+            python3-gst-1.0
 
       - name: Get changed lyrics files
         id: lyrics-update