Reinstate support for using list/tuple of `ViewSet`/`ViewSetGroup`s in `register_admin_viewset` (#11131)

wagtail/admin/viewsets/__init__.py

@@ -11,7 +11,11 @@ class ViewSetRegistry:
     def populate(self):
         for fn in hooks.get_hooks("register_admin_viewset"):
             viewset = fn()
-            self.register(viewset)
+            if isinstance(viewset, (list, tuple)):
+                for vs in viewset:
+                    self.register(vs)
+            else:
+                self.register(viewset)
 
     def register(self, viewset):
         # Allow registering a ViewSetGroup, which will register all of its

wagtail/test/testapp/wagtail_hooks.py

@@ -242,12 +242,7 @@ def add_broken_links_summary_item(request, items):
 
 @hooks.register("register_admin_viewset")
 def register_viewsets():
-    return MiscellaneousViewSetGroup()
-
-
-@hooks.register("register_admin_viewset")
-def register_json_model_viewsets():
-    return JSONModelViewSetGroup()
+    return [MiscellaneousViewSetGroup(), JSONModelViewSetGroup()]
 
 
 @hooks.register("register_admin_viewset")