The roundtrip in the handle-configure function could in theory (and in
practice in the future) happen to receive another configure event. If we
send yet another invalid geometry the second time, we log one time too
many in the server, which fails the test. Avoid this by ignoring the
second configure event; it's enough to pass through the error handling
path once.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1993>