PR: Fix regression in FORCE_QT_API behavior from merging PySide6 support

[tlambert03]

#225 somehow reverted the fix for the broken FORCE_QT_API that was fixed in #230. presumably a merge fail... not sure if there are others

on current master (this pretty much destroys environments with multiple Qt backends)

In [1]: import PySide6

In [2]: from qtpy import QtCore

In [3]: QtCore.QTimer
Out[3]: PyQt6.QtCore.QTimer

[CAM-Gerlach]

Good catch, @tlambert03 , thanks! LGTM, aside from the second (EDIT: and third) commit needing a fixup (and only if @dalthviz would rather not squash-merge it).

I was going to comment on the introduced typo (and clarify the comment a bit), but you fixed the former faster than I could do so, heh.

[CAM-Gerlach]

NB @dalthviz , the second and third commit either needs a fixup into the first, or the PR can simply be squash-merged, to clean up the duplicate, trivial commits.

[dalthviz]

Thanks @tlambert03 for noticing this and submitting a fix! LGTM 👍