testsuite: Add a gsk-compare-broadway suite

We have a Broadway renderer, might as well spell
that out in the tests, and make the suite exclude the
3d tests it can't handle.

testsuite/gsk/meson.build

@@ -80,6 +80,7 @@ informative_render_tests = [
 renderers = [
   # name      exclude term
   [ 'opengl', ''    ],
+  [ 'broadway',  '-3d' ],
   [ 'cairo',  '-3d' ],
 ]