Fixed #33044 -- Reallowed editable install into user site directory.

Regression in f8f35e8.

Author: carltongibson

setup.py

@@ -1,9 +1,14 @@
 import os
+import site
 import sys
 from distutils.sysconfig import get_python_lib
 
 from setuptools import setup
 
+# Allow editable install into user site directory.
+# See https://github.com/pypa/pip/issues/7953.
+site.ENABLE_USER_SITE = '--user' in sys.argv[1:]
+
 # Warn if we are installing over top of an existing installation. This can
 # cause issues where files that were deleted from a more recent Django are
 # still present in site-packages. See #18115.