fix: revert pypy 3.7 to 7.3.7

[henryiii]

See #1031

[henryiii]

For consistency, how about just rolling it back to consistently be 7.3.7 everywhere until manylinux and the issue with PyPy are fixed (probably in a 7.3.9)?

[henryiii]

Update: no, it looks like 3.9 is ready to go, so we could do 7.3.7 for 3.7, and 7.3.8 for 3.8 & 3.9. That would be fine.
Edit again: Forgot about manylinux, that won't have mixed PyPy versions, so back to liking consistent PyPy versions.

[mayeut]

@henryiii, manylinux is only rolling back 3.7 to 7.3.7: pypa/manylinux#1289

Update: no, it looks like 3.9 is ready to go, so we could do 7.3.7 for 3.7, and 7.3.8 for 3.8 & 3.9. That would be fine.

That plan works IMHO

[henryiii]

Happy to follow manylinux. We'll need a bump to the new manylinux images, so maybe we should just do everything in #1031.

[mayeut]

We'll need a bump to the new manylinux images, so maybe we should just do everything in #1031.

I was just about to propose that !