run-tests: send the test result after freeing the channel
Sending the message about the test being "done" signals to the main thread that
a new test can be started. Before this changeset, we sent this signal before
freeing the channel, there is room for a race condition where a new test would
search for a channel before the old test freed the one it used.
This is an example of the failure it would produce:
https://foss.heptapod.net/mercurial/mercurial-devel/-/jobs/552404
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).