Add support for PyPy3.9, drop PyPy3.7

[hugovk]

Like python-pillow/Pillow#6782.

Changes proposed in this pull request:

• PyPy v7.3.10 has been released
  • https://www.pypy.org/posts/2022/12/pypy-v7310-release.html
• Includes PyPy3.9 as a non-beta release:
  • "We have gained confidence in the stability of this version, and are removing the "beta" label."
• Drops PyPy3.7

---

Looks like we'll need an update to multibuild?

The Linux builds pass but the macOS don't because of a URL change:

  https://downloads.python.org/pypy/pypy3.8-v7.3.10-osx64.tar.bz2:
  2022-12-06 20:10:02 ERROR 404: Not Found.

https://github.com/hugovk/pillow-wheels/actions/runs/3632582399/jobs/6128598577

v7.3.9 had:

• pypy3.8-v7.3.9-osx64.tar.bz2

v7.3.10 has:

• pypy3.9-v7.3.10-macos_arm64.tar.bz2
• pypy3.9-v7.3.10-macos_x86_64.tar.bz2

https://downloads.python.org/pypy/

The release notes say it now includes both macOS versions:

Highlights of the release, since the release of 7.3.9 in March 2022 include:

• A release of Apple Silicon M1 arm64 versions. This work was sponsored by an anonymous donor and is tested on our buildbots.

[radarhere]

I've updated the x86_64 suffix in multi-build/multibuild#489

[radarhere]

I've created https://foss.heptapod.net/pypy/pypy/-/issues/3868 about the tkinter failure.

[radarhere]

It turns out that tkinter has been disabled on macOS PyPy - https://foss.heptapod.net/pypy/pypy/-/issues/3868#note_193028