Let the goToPage call afterwards to take precedence, instead
of resetting the adjustment (thus the view) on the side.
This resulted in strange state when the last page contains
a single icon, and it is dragged. The last page being emptied
triggers a pages-changed signal, which half resets the view
to the first page while DnD is ongoing.
Letting goToPage do its business means we neatly clamp to the
closest page to currentPage, the last page in that case.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1630>
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