Commit 83c6b2ab promisified the method in endSessionDialog, which means
that after the module is imported, every caller will get the promisifed
version. That can be a bit surprising in completely unrelated modules,
so commit 764527c8 (on master) moved the promisification of more common
methods into environment, as that's initialized early and expected to be
shared between anything else.
Do the same for the call() method on the stable branch.
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2551
654a7af929