Skip unit test on Fuchsia

Author: dcharkes

BUILD.gn

@@ -183,7 +183,6 @@ group("unittests") {
   # Compile all unittests targets if enabled.
   if (enable_unittests) {
     public_deps += [
-      "//flutter/assets:assets_unittests",
       "//flutter/display_list:display_list_rendertests",
       "//flutter/display_list:display_list_unittests",
       "//flutter/flow:flow_unittests",
@@ -215,6 +214,7 @@ group("unittests") {
 
     if (is_mac || is_linux || is_win) {
       public_deps += [
+        "//flutter/assets:assets_unittests",
         "//flutter/impeller:impeller_dart_unittests",
         "//flutter/impeller:impeller_unittests",
         "//flutter/impeller/toolkit/interop:example",