Use stable release of Django 6.0 for tests

Author: ulgens

tox.ini

@@ -38,7 +38,7 @@ deps =
     dj50: Django>=5.0,<5.1
     dj51: Django>=5.1,<5.2
     dj52: Django>=5.2,<5.3
-    dj60: Django>=6.0a1,<6.1  # Use a1 to allow testing of the release candidates
+    dj60: Django>=6.0,<6.1
     djmain: https://github.com/django/django/tarball/main
     postgres: -rrequirements/postgres.txt
     mysql: -rrequirements/mysql.txt