ci: install Linux build deps (libgtk-3-dev etc.)

.github/workflows/build.yml

@@ -17,10 +17,10 @@ jobs:
         with:
           channel: stable
 
-      - name: Install packaging tools
+      - name: Install Linux dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y patchelf fakeroot dpkg
+          sudo apt-get install -y libgtk-3-dev ninja-build clang cmake pkg-config patchelf fakeroot dpkg
 
       - name: Get dependencies
         run: flutter pub get