Install Ruby before fpm in CI

.github/workflows/release.yml

@@ -28,8 +28,11 @@ jobs:
         ls -la /lib/x86_64-linux-gnu/libpython* 2>/dev/null || echo "Not found in /lib"
     - name: Build binary
       run: pyinstaller gotify-tray.spec
-    - name: Install fpm
-      run: gem install fpm
+    - name: Install Ruby and fpm
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y ruby-full
+        gem install fpm
     - name: Build Debian package
       run: |
         mkdir -p build/linux/opt