Add coverage upload step in ci

.github/workflows/ci.yml

@@ -32,4 +32,7 @@ jobs:
         run: flutter analyze --fatal-infos
 
       - name: Run tests
-        run: flutter test
+        run: flutter test --coverage
+
+      - name: Upload coverage
+        uses: codecov/codecov-action@v3

.gitignore

@@ -75,4 +75,6 @@ build/
 !/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages
 
 .vscode/
-example/lib/debug.dart
+example/lib/debug.dart
+
+coverage/