Release build_runner 2.9.0, build 4.0.1.

[davidmorgan]

Release the bootstrap refactoring before the AOT compilation it's there to allow, so we have a better chance to detect if I broke/regressed anything.

Fix a typo in build API docs.

Release build (API docs) and build_test (pins to build+build_runner).

[github-actions]

PR Health

Changelog Entry ✔️

Package	Changed Files

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

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[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:build	4.0.1	ready to publish	build-v4.0.1
package:build_config	1.2.0	already published at pub.dev
package:build_daemon	4.0.5-wip	WIP (no publish necessary)
package:build_modules	5.0.18	already published at pub.dev
package:build_runner	2.9.0	ready to publish	build_runner-v2.9.0
package:build_test	3.4.1	ready to publish	build_test-v3.4.1
package:build_web_compilers	4.2.4	already published at pub.dev
package:scratch_space	1.1.1	already published at pub.dev

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