testsuite: Hey, everyone has an NGL renderer, right?

No.

This fix is not that much better, but I'm too tired to fix stuff
like this properly.

And the Cairo renderer did at least work everywhere during 4.x

testsuite/gsk/normalize.c

@@ -6,7 +6,7 @@ static void
 test_normalize (GskRenderNode *node1,
                 GskRenderNode *node2)
 {
-  GskRenderer *renderer = gsk_ngl_renderer_new ();
+  GskRenderer *renderer = gsk_cairo_renderer_new ();
   graphene_rect_t bounds1, bounds2;
   GdkTexture *texture1, *texture2, *diff;
   GError *error = NULL;