added flutter clean / pub get lines before release build lines to resolve errors in release workflow (#1147)

.github/workflows/release.yaml

@@ -34,7 +34,11 @@ jobs:
       - name: Prepare web
         run: ./scripts/prepare-web.sh
       - name: Build Release Web
-        run: flutter build web --dart-define=FLUTTER_WEB_CANVASKIT_URL=canvaskit/ --release --source-maps
+        run: |
+          flutter config --enable-web
+          flutter clean
+          flutter pub get
+          flutter build web --dart-define=FLUTTER_WEB_CANVASKIT_URL=canvaskit/ --release --source-maps
       - name: Create archive
         run: tar -czf pangeachat-web.tar.gz build/web/
       - name: Upload Web Build