Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=54037

test_SendMessage_other_thread(2), which is supposed to show that
Windows doesn't use an internal sent message for SetParent, tacks
this onto another more complex test, which introduces a race
condition (see Comment 2 on the bug). I am not sure if it can be
fixed in the existing function, perhaps it can and I just can't
keep track of all the moving parts well enough, but I see no need
to make it so difficult.