Shutting down daemon process if build_runner throws.

[Markzipan]

Consecutive execution of webdev serve when build_runner throws was causing an errant VM process to hold onto websocket connections, resulting in:

WebSocketChannelException: SocketException: Connection refused (OS Error: Connection refused, errno = 61), address = localhost, port = XXXXX

[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	4.0.2	already published at pub.dev
package:build_config	1.2.0	already published at pub.dev
package:build_daemon	4.1.1	ready to publish	build_daemon-v4.1.1
package:build_modules	5.1.1	already published at pub.dev
package:build_runner	2.10.3-wip	WIP (no publish necessary)
package:build_test	3.5.3-wip	WIP (no publish necessary)
package:build_web_compilers	4.4.1	already published at pub.dev
package:scratch_space	1.2.0	already published at pub.dev

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

[davidmorgan]

Thanks :)