xwl_present_reset_timer checks if the pending flip is synchronous, so
we need to call it after adding the pending flip to the flip queue.
Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1219
Fixes: b2a06e0700 "xwayland/present: Drop sync_flip member of struct xwl_present_window"
Tested-by: Olivier Fourdan <ofourdan@redhat.com>
Acked-by: Olivier Fourdan <ofourdan@redhat.com>