See https://github.com/flutter/flutter/issues/159154.
See https://github.com/flutter/flutter/pull/159169.
Before this PR, it appeared we were accidentally leaking (keeping
active) `flutter_tester` instances (or any test device) after `flutter
run` completion, even if the runner was not explicitly detached. I
_think_ this is a bug, but I'll check with the tools team and possibly
@jonahwilliams before finalizing this.
/cc @jason-simmons
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Co-authored-by: Andrew Kolos <andrewrkolos@gmail.com>
