tests: avoid g_test_add_data_func_full
tests: avoid g_test_add_data_func_full

That function has been introduced in GLib 2.34, so depending on it
effectively added a hard dependency on that GLib version for testing.

I moved to g_test_add_data_func() instead: that update was trivial
and did not add the dependency.

ntd/adg,ntd/adg