Update dependency flutter_lints to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
flutter_lints (source)	dev_dependencies	major	^1.0.4 → ^6.0.0

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Release Notes

flutter/packages (flutter_lints)

v6.0.0

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v5.0.0

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v4.0.0

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v3.0.2

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• Updates minimum supported SDK version to Flutter 3.13/Dart 3.1.
• Updates various links in comments and documentation.

v3.0.1

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• Replaces flutter pub add --dev with dev: in README.md.

v3.0.0

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v2.0.3

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• Adds pub topics to package metadata.
• Updates minimum supported SDK version to Flutter 3.7/Dart 2.19.

v2.0.2

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• Update links to the old linter site in the README and example to point to dart.dev.
• Updates minimum supported SDK version to Flutter 3.3/Dart 2.18.

v2.0.1

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• Updated readme to document suggestion process for new lints

v2.0.0

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• Added the following lints:
  • sort_child_properties_last
  • use_build_context_synchronously
• Updated package:lints dependency to version 2.0.0, which added the following lints:
  • depend_on_referenced_packages
  • library_private_types_in_public_api
  • no_leading_underscores_for_library_prefixes
  • no_leading_underscores_for_local_identifiers
  • null_check_on_nullable_type_parameter
  • prefer_interpolation_to_compose_strings
  • unnecessary_constructor_name
  • unnecessary_late
  • unnecessary_null_aware_assignments
  • unnecessary_nullable_for_final_variable_declarations
• Bumped the minimum required Dart SDK version to 2.17

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