fix: Update Linux integration test step to use setup-xvfb action for improved execution

Author: oldrev

.github/workflows/flutter-ci.yml

@@ -66,10 +66,9 @@ jobs:
         run: sudo apt-get update && sudo apt-get install -y xvfb libgtk-3-dev libstdc++-12-dev
 
       - name: Run linux integration tests
-        if: runner.os == 'Linux'
-        # desktop integration tests run on the same container; wrap in Xvfb
-        run: |
-          xvfb-run flutter test integration_test/app_test.dart -d linux
+        uses: coactions/setup-xvfb@v1
+        with:
+          run: flutter test integration_test/app_test.dart -d linux -r github
 
   build-apk:
     needs: test