fix: Update flame_lint to use lints 6.0.0

[spydon]

Description

[!NOTE] Can't be merged until we've bumped to SDK 3.8.0

Update flame_lint to use lints 6.0.0

Checklist

• [x] I have followed the Contributor Guide when preparing my PR.
• [x] I have updated/added tests for ALL new/updated/fixed functionality.
• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [x] I have updated/added relevant examples in examples or docs.

Breaking Change?

• [ ] Yes, this PR is a breaking change.
• [x] No, this PR is not a breaking change.

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