test_glib: Drop some assumptions about XDG dirs
test_glib: Drop some assumptions about XDG dirs

Some directories do not exist in minimal test environments, and this is not
important for testing that calling these GLib functions works.

pexip/pygobject,GNOME/pygobject,sfeltman/pygobject,GNOME/pygobject,sfeltman/pygobject,pexip/pygobject,sfeltman/pygobject,davibe/pygobject,pexip/pygobject,GNOME/pygobject,davibe/pygobject,davibe/pygobject,davibe/pygobject