Add one more mock to flaky map list

Author: camdecoster

test/image/compare_pixels_collections.json

@@ -11,7 +11,11 @@
     "map_stamen-style"
   ],
   "flaky": ["gl3d_bunny-hull"],
-  "flaky_maps": ["map_density0-legend", "map_predefined-styles1"],
+  "flaky_maps": [
+    "map_density0-legend",
+    "map_fonts-supported-metropolis-italic",
+    "map_predefined-styles1"
+  ],
   "flaky_virtual_webgl": [
     "gl2d_parcoords_256_colors",
     "gl2d_parcoords_coloraxis",