[BUG] setuptools 60.3.0 breaks pip on Ubuntu 20.04.3

[Patol75]

setuptools version

setuptools==60.3.0

Python version

Python 3.9

OS

Ubuntu 20.04.3 LTS

Additional environment information

No response

Description

Updating setuptools from 60.2.0 to 60.3.0 yields the following error message after executing any python3.9 -m pip command:
/usr/bin/python3.9: Error while finding module specification for 'pip' (AttributeError: module '__main__' has no attribute '__file__')

Expected behavior

Updating setuptools should not break pip.

How to Reproduce

Simply update setuptools to the last release and attempt to use pip.

Output

python3.9 -m pip install --user --upgrade setuptools
/usr/bin/python3.9: Error while finding module specification for 'pip' (AttributeError: module '__main__' has no attribute '__file__')

Code of Conduct

• I agree to follow the PSF Code of Conduct

[matthewfeickert]

👋 This is a duplicate of Issue #3002, so please follow along there for new information and consider closing this Issue to avoid confusion. 👍

[Patol75]

Unfortunate timing on my side it seems, #3002 was not opened when I started writing this issue. Anyway, good to know I am not the only one and developers are aware of the issue. :)