bug#73816: python-django's manage.py tries to use a hard-coded python executable

[Gabriel Wicki]

The python-django package makes the admin utility create a manage.py
file with a hard-coded python interpreter.

  $ guix shell python python-django -- django-admin startproject foobar
  $ head -n 1 foobar/manage.py
  
#!/gnu/store/my2j5bzapayk59971z2ryzlajdz569f9-python-toolchain-3.10.7/bin/python

I think this is wrong.  The interpreter line should be

  #!/usr/bin/env python3

Or am I wrong?