The h2 server is running in a separate thread, so while the previous
test was finished and the server was deleted, it could still emit
and have a queued emission in-flight which would be picked up by
the next running test.
Pick-to: 6.2 6.1 5.15
Change-Id: I26b1bc711df7473032d6078f35f8aca37c40137e
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>