Refs #27728 -- Fixed thread safety of admin template tags.

Regression in 5cc28dc7.

django/contrib/admin/templatetags/base.py

@@ -23,10 +23,11 @@ class InclusionAdminNode(InclusionNode):
         opts = context['opts']
         app_label = opts.app_label.lower()
         object_name = opts.object_name.lower()
-        self.filename = [
+        # Load template for this render call. (Setting self.filename isn't
+        # thread-safe.)
+        context.render_context[self] = context.template.engine.select_template([
             'admin/%s/%s/%s' % (app_label, object_name, self.template_name),
             'admin/%s/%s' % (app_label, self.template_name),
             'admin/%s' % (self.template_name,),
-        ]
-
+        ])
         return super().render(context)