Warning due to PEP660 editable packages

[fschulze]

The recently added PEP660 support for editable package installs seems to interfere with assert rewriting. I get the following warning:

PytestAssertRewriteWarning: Module already imported so cannot be rewritten: __editable__...

This seems to be caused by the new __editable__* files in site-packages.

If I install the editable packages with --no-use-pep517 the __editable__* files aren't generated and the warnings are gone.

[RonnyPfannschmidt]

closing as dupe of #10230 , which is easy to miss as the same

[fschulze]

I actually saw that and didn't realize it has the same cause.