Update dependency django-stubs to v4

Author: renovate[bot]

pyproject.toml

@@ -82,7 +82,7 @@ psycopg2 = {version = "=2.9.6", python = "3.6.* || 3.7.* || 3.8.* || 3.9.*"}
 mysqlclient = {version = "=2.1.1", python = "^3.6"}
 tox = "^3.25"
 mypy = {version = "^0.961", python = "^3.6"}
-django-stubs = {version = "^1.9", python = "^3.6"}
+django-stubs = {version = "^4.0.0", python = "^3.6"}
 
 [tool.poetry.extras]
 deploy = ["bump2version", "git-changelog"]