[BUG] python setup.py develop/install installs package in site-packages, but only dist-packages is on path

setuptools version

67.6.1

Python version

Python 3.8

OS

Ubuntu 20:04

Additional environment information

Using python 3.8 installed via apt-get.

Description

Installing a package via python setup.py develop/install on ubuntu:20.04, results in the package being installed to the wrong place, site-packages instead of dist-packages

I've confirmed previous versions of setuptools correctly install things to dist-packages (45.2.0)

Expected behavior

Running python setup.py install makes the package importable

How to Reproduce

python setup.py install with the system python on ubuntu:20.04

Output

+ python3 setup.py develop
running develop
/usr/local/lib/python3.8/dist-packages/setuptools/command/develop.py:40: EasyInstallDeprecationWarning: easy_install command is deprecated.
!!

        ********************************************************************************
        Please avoid running ``setup.py`` and ``easy_install``.
        Instead, use pypa/build, pypa/installer, pypa/build or
        other standards-based tools.

        See https://github.com/pypa/setuptools/issues/917 for details.
        ********************************************************************************

!!
  easy_install.initialize_options(self)
/usr/local/lib/python3.8/dist-packages/setuptools/_distutils/cmd.py:66: SetuptoolsDeprecationWarning: setup.py install is deprecated.
!!

        ********************************************************************************
        Please avoid running ``setup.py`` directly.
        Instead, use pypa/build, pypa/installer, pypa/build or
        other standards-based tools.

        See https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html for details.
        ********************************************************************************

!!
  self.initialize_options()
running egg_info
writing egg_link_package.egg-info/PKG-INFO
writing dependency_links to egg_link_package.egg-info/dependency_links.txt
writing top-level names to egg_link_package.egg-info/top_level.txt
reading manifest file 'egg_link_package.egg-info/SOURCES.txt'
writing manifest file 'egg_link_package.egg-info/SOURCES.txt'
running build_ext
Creating /usr/lib/python3.8/site-packages/egg-link-package.egg-link (link to .)
Adding egg-link-package 0.1.3 to easy-install.pth file

Installed /workdir/integration-tests/package-sync/dummy-packages/egg_link_package
Processing dependencies for egg-link-package==0.1.3
Finished processing dependencies for egg-link-package==0.1.3

Start with setuptools/command/develop.py around line 40 and reproduce the setup.py install or develop command using system Python 3.8 on Ubuntu 20.04. Trace why the egg-link is created under site-packages instead of dist-packages; done means the installed package is importable through the system Python path and existing behavior is preserved for supported environments.