pip deprecation: In the future local packages will be built in-place without first copying to a temp dir

[carlosperate]

20211005 170630 I pup.plugins.pip_install About to run '/Users/runner/work/mu/mu/build/pup/Mu Editor.app/Contents/Resources/Python/bin/python3.8 -m pip install --no-warn-script-location .'.
20211005 170633 I pup.plugins.pip_install pip out: Processing /Users/runner/work/mu/mu
20211005 170633 I pup.plugins.pip_install pip err:   DEPRECATION: A future pip version will change local packages to be built in-place without first copying to a temporary directory. We recommend you use --use-feature=in-tree-build to test your packages with this new behavior before it becomes the default.
20211005 170633 I pup.plugins.pip_install pip err:    pip 21.3 will remove support for this functionality. You can find discussion regarding this at https://github.com/pypa/pip/issues/7555.

Hopefully it shoudn't affect pup, but this might pollute the local mu project directory, not sure if that'll be an issue.
Were you aware of this @tmontes?