Allow analyzer 9.

[davidmorgan]

Fix #4286

[github-actions]

PR Health

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

This check can be disabled by tagging the PR with skip-changelog-check.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:build	4.0.3	ready to publish	build-v4.0.3
package:build_config	1.2.0	already published at pub.dev
package:build_daemon	4.1.1	already published at pub.dev
package:build_modules	5.1.3	ready to publish	build_modules-v5.1.3
package:build_runner	2.10.4	ready to publish	build_runner-v2.10.4
package:build_test	3.5.4	ready to publish	build_test-v3.5.4
package:build_web_compilers	4.4.2	(error) pubspec version (4.4.2) and changelog (4.4.3) don't agree
package:scratch_space	1.2.0	already published at pub.dev

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