FIX: update can_see_members attribute after leaving a group. (#15982)

After leaving a group, it is trying to reload its member list. Previously, when the members_visibility_level attribute has a value of 2 or higher, it displayed an error popup since the can_see_members attribute was not updated.

app/assets/javascripts/discourse/app/models/group.js

@@ -124,6 +124,7 @@ const Group = RestModel.extend({
     await ajax(`/groups/${this.id}/leave.json`, {
       type: "DELETE",
     });
+    this.set("can_see_members", this.members_visibility_level < 2);
     await this.reloadMembers({}, true);
   },