fix(hero prefab): add missing instance and targetOverrides fields

补充所有hero预制体中缺失的instance和targetOverrides空值字段，完善预制体配置结构

assets/resources/gui/element/hero.prefab

@@ -2378,6 +2378,8 @@
       "__id__": 0
     },
     "fileId": "5cPMX9Mf1EUKu4iFbzdDQG",
+    "instance": null,
+    "targetOverrides": null,
     "nestedPrefabInstanceRoots": null
   },
   {
@@ -2992,6 +2994,8 @@
       "__id__": 0
     },
     "fileId": "95cG7XB6lJIpMUYj+ecR3n",
+    "instance": null,
+    "targetOverrides": null,
     "nestedPrefabInstanceRoots": null
   },
   {
@@ -3606,6 +3610,8 @@
       "__id__": 0
     },
     "fileId": "d47n3iZV1DQavg7IXRtMpG",
+    "instance": null,
+    "targetOverrides": null,
     "nestedPrefabInstanceRoots": null
   },
   {
@@ -4220,6 +4226,8 @@
       "__id__": 0
     },
     "fileId": "84/ESDOKlOIptfoG9+jEsU",
+    "instance": null,
+    "targetOverrides": null,
     "nestedPrefabInstanceRoots": null
   },
   {