ci: Use fixed version of flutter-action

[Gustl22]

Description

Like in flame it is more practicable to use fixed version of flutter-action to avoid unexpected failures of the CI.

Further when flutter is releasing a new version, one should upgrade the version of flutter-action and also add the required changes to pass the tests at the same time.

This ensures that the tests in the main always stay consistent. It also makes the development faster and more independent of other packages such as flame-lint.

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs:, chore: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation and added dartdoc comments with ///, where necessary.
• I have updated/added relevant examples in example.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Related Issues

flame-engine/flame#2532