fix: test for v3

Author: fsbraun

djangocms_frontend/ui_plugin_base.py

@@ -19,6 +19,9 @@ class FrontendEditableAdminMixin:
     # django CMS 3 did not implement this: use our own version of the plugin-enabled mixin
     from .helpers import FrontendEditableAdminMixin
 
+    class PlaceholderAdmin:
+        pass
+
 
 class CMSUIPluginBase(FrontendEditableAdminMixin, CMSPluginBase):
     render_template = "djangocms_frontend/html_container.html"