PyPy has released bug fixes and a python3.9

[mattip]

Description

PyPy released version v7.3.8. It would be nice to be able to use it in cibuildwheel, including the newly released python3.9

Build log

No response

CI config

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[mayeut]

Bug fixes are included in #1027 (for macOS/Windows).
PyPy 3.9 is addressed in #1031 (for macOS/Windows).
manylinux is on hold for both c.f. pypa/manylinux#1288 (comment)