Sometimes on aarch64 clicking the partition scheme drop-down
just doesn't seem to make the menu appear, instead the button
goes active but that's all. It's very unlikely we'll be able
to track down why as this doesn't happen in manual testing on
aarch64 (according to @pwhalen), so instead let's just work
around it.
Signed-off-by: Adam Williamson <awilliam@redhat.com>
