chore(deps): update dependency flutter_lints to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
flutter_lints (source)	dependencies	major	^5.0.0 -> ^6.0.0

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Release Notes

flutter/packages (flutter_lints)

v6.0.0

Compare Source

• Updates package:lints dependency to version 6.0.0, with the following changes:
  • adds strict_top_level_inference
  • adds unnecessary_underscores
• Updates minimum supported SDK version to Flutter 3.32/Dart 3.8.

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