Added local copy of Django to deps in tox.ini.

This also bumps tox to 4.0.

tox.ini

@@ -4,7 +4,7 @@
 # then run "tox" from this directory.
 
 [tox]
-minversion = 3.18
+minversion = 4.0
 skipsdist = true
 envlist =
     py3
@@ -25,6 +25,7 @@ passenv = DJANGO_SETTINGS_MODULE,PYTHONPATH,HOME,DISPLAY,OBJC_DISABLE_INITIALIZE
 setenv =
     PYTHONDONTWRITEBYTECODE=1
 deps =
+    -e .
     py{3,310,311}: -rtests/requirements/py3.txt
     postgres: -rtests/requirements/postgres.txt
     mysql: -rtests/requirements/mysql.txt