Flutter Action Versions Save

This release introduces the dry-run option, which lets you only get action outputs without downloading Flutter. This can be useful if you want to set up some automations to be notified about new Flutter releases.

steps:
  - name: Clone repository
  - uses: actions/checkout@v4
  - name: Set up Flutter
    uses: subosito/flutter-action@v2
    id: flutter-action
    with:
      channel: stable
      dry-run: true
  - run: |
      # Always print the latest stable version.
      echo CHANNEL=${{ steps.flutter-action.outputs.CHANNEL }}
      echo VERSION=${{ steps.flutter-action.outputs.VERSION }}
    shell: bash

Thank you @kzrnm for suggesting and implementing it in #270!

Hi! I'm Bartek and I'm a new maintainer of this action. I promise to take good care of it.

This release introduces the flutter-version-file option (implemented in #290), which lets you easily centralize Flutter version in a single place – your pubspec.yaml file:

You can use it like this:

steps:
  - name: Clone repository
    uses: actions/checkout@v4
  - name: Set up Flutter
    uses: subosito/flutter-action@v2
    with:
      channel: stable
      flutter-version-file: pubspec.yaml # path to pubspec.yaml

Please note that for this to work, you need to specify exact Flutter version in pubspec.yaml:

environment:
  dart: ">=3.3.0 <4.0.0"
  flutter: 3.19.0 # This must be exact! No ranges allowed.

Apart from that, some minor README updates and code cleanup were performed.

Allow git ref as version for master channel:

steps:
- uses: actions/checkout@v3
- uses: subosito/flutter-action@v2
  with:
    flutter-version: '5b12b74' # tag, commit or branch
    channel: 'master'
- run: flutter --version

• Rewrite to make simpler
• Drop master channel
• Drop searching for a version with a v-prefix query, use, e.g, 0.11.9 instead of v0.11.9
• Support restore keys for cache