Flutter hint in the documentation

On creating a new action, there is some hint about being used with Flutter

```
# Your project will need to have tests in test/ and a dependency on
# package:test for this step to succeed. Note that Flutter projects will
# want to change this to 'flutter test'.
- name: Run tests
run: dart test
```

And since my project is actually Flutter, changing this to `flutter test`, gives the error

>Flutter users should run `flutter pub get` instead of `dart pub get`.

And on changing the action to `flutter pub get` there is an error

>flutter: command not found

I guess this action is for Dart, not Flutter. In this case, please change the action comments accordingly.

Start from the documentation or new-action example containing the shown Dart test workflow and Flutter hint. Check whether Flutter is supported by this action, then revise the comments to describe the supported Dart commands accurately and verify the rendered documentation example.

Written by the indexing model from the issue text.