Fixed defaultValue for sharedViews setting

refs https://github.com/TryGhost/Ghost/issues/10318

- `shared_views` is always an array (Ghost-Admin has handling to revert it to an array if it's anything else) but it's default value was set to an empty object

core/server/data/schema/default-settings.json

@@ -239,7 +239,7 @@
     },
     "views": {
         "shared_views": {
-            "defaultValue": "{}"
+            "defaultValue": "[]"
         }
     }
 }