tests: Fix metrolyrics test not finding the source
tests: Fix metrolyrics test not finding the source

The lua sources aren't compiled, so they live in srcdir, not builddir.

MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,GNOME/grilo-plugins,MathieuDuponchelle/grilo-plugins,GNOME/grilo-plugins,MathieuDuponchelle/grilo-plugins,jasuarez/grilo-plugins,jasuarez/grilo-plugins