Set DJANGO_SETTINGS_MODULE in django-serve justfile recipe

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: aclark4life

src/dbx_python_cli/templates/project_template/justfile

@@ -10,7 +10,7 @@ alias o := django-open
 
 [group('django')]
 django-serve:
-    python manage.py runserver
+    DJANGO_SETTINGS_MODULE={{ project_name }}.settings.{{ project_name }} python manage.py runserver
 
 [group('django')]
 django-migrate: