* Revert to prior build-system requirements
This reverts #14080.
* Use normalised extra name, which poetry-core 1.3 will generate anyway
* Changelog
* Upper bound build-system requirements
* Remove upgrade note; expand changelog entry a little.
* Fix typo in build-system comment
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>