Update to PyPy 7.3.4

[YannickJadoul]

Hurray for another PyPy release! :-)

Changes aside from just replacing 7.3.3 with 7.3.4:

• The tarballs now already seem to include python symlinks, so I'm checking that before actually creating the symlink.
• Python 3.6 isn't provided anymore. Which reminds me: I should still update the README, in a bit! EDIT: Done

[asottile]

[mayeut]

@asottile,

Is anything blocking for this PR ?

It's needed for 3 on going PRs for cibuildwheel and would be very much appreciated if it can get merged in.

Maybe it's worth waiting for 7.3.5 ?

For 2 of the PRs over at cibuildwheel, a simple rebuild of the current image would probably be enough (i.e. they require an up-to-date base manylinux2010 image). I can do another PR just for this if this is the preferred approach.

[asottile]

ah nope, when I approved it I think it was still building

[mayeut]

thanks @asottile