Bump codecov/codecov-action from 5.3.1 to 5.4.0 in /.github/workflows (#309)

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 5.3.1 to 5.4.0.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v5.3.1...v5.4.0)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/testing.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Run Tests
         run: flutter test --coverage
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v5.3.1
+        uses: codecov/codecov-action@v5.4.0
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           files: coverage/lcov.info