Prepare to publish build_web_compilers

[natebosch]

Bump the SDK upper constraint to allow the SDK version bump.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:build_web_compilers	4.0.8	ready to publish	build_web_compilers-v4.0.8
package:build	2.4.2-wip	WIP (no publish necessary)
package:build_config	1.1.2-wip	WIP (no publish necessary)
package:build_daemon	4.0.1	already published at pub.dev
package:build_modules	5.0.5	already published at pub.dev
package:build_resolvers	2.4.2	already published at pub.dev
package:build_runner	2.4.8-wip	WIP (no publish necessary)
package:build_runner_core	7.2.12-wip	WIP (no publish necessary)
package:build_test	2.2.2	already published at pub.dev
package:scratch_space	1.0.3-wip	WIP (no publish necessary)

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

[elliette]

Thank you!

[natebosch]

I've hit multiple flakes with some browser tests (we've seen these before) and it looks like a flake takes a reallly long time to finish. I'm going to merge on red CI for now.