Fixed invalid escape sequence warning in check_framework test.

tests/check_framework/urls/path_compatibility/contains_re_named_group.py

@@ -1,5 +1,5 @@
 from django.urls import path
 
 urlpatterns = [
-    path('(?P<named-group>\d+)', lambda x: x),
+    path(r'(?P<named-group>\d+)', lambda x: x),
 ]