Create Flutter Test Report

Usage

- name: flutter test
  run: flutter test --machine > test.json
- name: flutter test
  run: flutter test --coverage
  if: success() || failure()
- uses: ueki-tomohiro/flutter-test-action@v1
  with:
    machinPath: test.json
    coveragePath: coverage/lcov.info
  if: success() || failure()