The last commit improved the heuristics for detecting network mounts,
but at the price of potentially blocking the shell. Avoid that drawback
by making the code in question async.
https://gitlab.gnome.org/GNOME/gnome-shell-extensions/issues/53
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/27>
(cherry picked from commit 519269be9d)