rev to 3.0.0; prep to publish

[devoncarew]

• rev to 3.0.0; prep to publish

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• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:lints	3.0.0	ready to publish	v3.0.0

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[goderbauer]

LGTM