tests: Add tests for GArray constructors
tests: Add tests for GArray constructors

Noticed these were missing when handling bug #733648. Add a few missing
tests to improve coverage.

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib