js: Update for Gio/GioUnix split
GLib 2.79.2 split out the platform specific Gio APIs into a separate GIRs, while still keeping a copy in the Gio GIR. gjs then added warnings about the APIs being moved.
This bumps the Gio(Unix) version requirement to 2.79.2 and switches to using the new GioUnix GIR.
See: glib!3892 (merged) See: gjs!918 (merged) Closes: #7539 (closed)