Update dependency file_picker to v8

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
file_picker (source)	dependencies	major	^6.1.1 -> ^8.0.0

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Release Notes

miguelpruivo/flutter_file_picker (file_picker)

### [`v8.0.0+1`](https://togithub.com/miguelpruivo/flutter_file_picker/blob/HEAD/CHANGELOG.md#8001) [Compare Source](https://togithub.com/miguelpruivo/flutter_file_picker/compare/8.0.0...8.0.0) Removes linter warnings and fixes CI/CD. ### [`v8.0.0`](https://togithub.com/miguelpruivo/flutter_file_picker/blob/HEAD/CHANGELOG.md#8001) [Compare Source](https://togithub.com/miguelpruivo/flutter_file_picker/compare/7.1.0...8.0.0) Removes linter warnings and fixes CI/CD. ### [`v7.1.0+1`](https://togithub.com/miguelpruivo/flutter_file_picker/blob/HEAD/CHANGELOG.md#7101) [Compare Source](https://togithub.com/miguelpruivo/flutter_file_picker/compare/7.1.0...7.1.0) Fixes typo on docs (there was some refernces to `FileType.all` instead of the correct `FileType.any`). ### [`v7.1.0`](https://togithub.com/miguelpruivo/flutter_file_picker/blob/HEAD/CHANGELOG.md#7101) Fixes typo on docs (there was some refernces to `FileType.all` instead of the correct `FileType.any`). ### [`v7.0.2`](https://togithub.com/miguelpruivo/flutter_file_picker/blob/HEAD/CHANGELOG.md#702) ##### Desktop (Linux) - File picker extensions for Linux Zenity are case insensitive now - Fixes [#​1322](https://togithub.com/miguelpruivo/flutter_file_picker/issues/1322)

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