Use PyPI Trusted Publishers feature to publish releases

[bluetech]

https://docs.pypi.org/trusted-publishers/

This is currently still in beta, and I don't think pytest should be a beta tester, but opening this issue for discussion ahead of time.

Seems like a good improvement over the API token method we currently use.

[nicoddemus]

Indeed, looks like a good improvement, thanks for reporting it. 👍

[RonnyPfannschmidt]

I'll play early adoption in setuptools_scm and execnet, then we can transfer to pytest*

[RonnyPfannschmidt]

@nicoddemus @bluetech i just made a test mr to setuptools_scm testing it, it works fabulous and is absolutely easy

i'll add some extras for setuptools_scm so that we can have test-pypi uploads and then propose the change to pytest either this or next week

[bluetech]

@RonnyPfannschmidt nice!