fix usage of font_metadata condition on the self-tests
fix usage of font_metadata condition on the self-tests

(issue #1539)

graphicore/fontbakery,moyogo/fontbakery,graphicore/fontbakery,googlefonts/fontbakery,googlefonts/fontbakery,googlefonts/fontbakery,moyogo/fontbakery,moyogo/fontbakery,graphicore/fontbakery