chore(deps): update dependency wagtail to v4 [security]

Author: renovate[bot]

requirements.txt

@@ -310,7 +310,7 @@ vine==5.0.0
     #   amqp
     #   celery
     #   kombu
-wagtail==2.12.5
+wagtail==4.1.9
     # via -r requirements.in
 wcwidth==0.1.7
     # via prompt-toolkit