Building wheels for python 3.9

[Israel Fruchter]

I'm doing builds base on fedora34, which has python3.9, both on aarch64 and x86_64, and not having wheel for those, is slowing down a lot builds with qemu based cross compilation (building docker for both architectures)

[Paul Kehrer]

Our wheels work fine on python 3.9 for x86_64. aarch64 wheels will be coming in the next release.

[Alex Gaynor]

https://cryptography.io/en/latest/faq/#why-are-there-no-wheels-for-my-python3-x-version