Corrected error in settings.py

missing comma after "celery" caused failed tests

devproject/settings.py

@@ -169,7 +169,7 @@ INSTALLED_APPS = [
     "django.contrib.messages",
     "django.contrib.staticfiles",
     # 3rd party apps used by Misago
-    "celery"
+    "celery",
     "debug_toolbar",
     "mptt",
     "rest_framework",