fix(webview): update GTK lifecycle cleanup and repeat Linux integration tests

.github/workflows/test.yml

@@ -77,6 +77,8 @@ jobs:
         include:
           - name: Windows
             os: windows-latest
+          - name: Linux
+            os: ubuntu-latest
           - name: macOS
             os: macos-latest
     runs-on: ${{ matrix.os }}
@@ -89,6 +91,17 @@ jobs:
         if: runner.os == 'macOS'
         with:
           flutter-version: ${{ env.FLUTTER_VERSION }}
+      - name: Install Linux WebView dependencies
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt-get update -y
+          sudo apt-get install -y libgtk-3-dev libwebkit2gtk-4.1-dev xvfb
+      - name: Test webview
+        if: runner.os == 'Linux'
+        # Repeat on the same GTK event loop to catch callbacks after destruction.
+        run: xvfb-run -a go test -tags webview -v -count=5 -timeout 300s ./internal/webview/goprovider/
+        env:
+          CGO_ENABLED: 1
       - name: Test webview
         if: runner.os == 'Windows'
         # Repeat close/reopen coverage to catch browser shutdown races.