ci: Add a build with G_DISABLE_ASSERT defined
ci: Add a build with G_DISABLE_ASSERT defined

We want GLib to build correctly with this defined, and for all its tests
to still pass.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #1708

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib