Update subosito/flutter-action action to v2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
subosito/flutter-action	action	major	v1 -> v2

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Release Notes

subosito/flutter-action

### [`v2`](https://togithub.com/subosito/flutter-action/compare/v1...v2) [Compare Source](https://togithub.com/subosito/flutter-action/compare/v1...v2)

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Configuration

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