Comment 7 for bug 1912248

I have verified fix in amd64 xenial VM.

Test case:

* `sudo apt install python3-virtualenv virtualenv python-virtualenv`
* Confirm that any `pip` operations fail as per bug description
  * `virtualenv -p /usr/bin/python3 venv/py3 --verbose`
  * `source ./venv/py3/bin/activate`
  * `pip list`
* Enable proposed as per https://wiki.ubuntu.com/Testing/EnableProposed
* Upgrade packages using `sudo apt install python3-virtualenv virtualenv python-virtualenv`
* Confirm that any `pip` operations succeed
  * `virtualenv -p /usr/bin/python3 venv/py3-verification --verbose`
    * I also confirm here that the pip and setup tools were being pinned here
      > Installing setuptools < 51.3, pkg_resources, pip < 21, wheel...
  * `source ./venv/py3-verification/bin/activate`
  * `pip list`

Tags added verification-done-xenial verification-done