meson: Fix typo in gobject dependency name
This worked fine by accident, but fails when you try to use glib as a subproject:
glib-networking/meson.build:50:0: ERROR: Inconsistency: Subproject has overriden the dependency with another variable than 'libgobject_dep'
I'd like to cherry-pick this into glib-2-62 and glib-2-64.