Include RISCV64 build for 2.2.1

[mtelvers]

It would be excellent if a precompiled binary was available for 2.2.1 (current release) for riscv64.

The documentation says that there is a riscv64 binary available. see here

I can see that one will be available in the 2.3.0 series as it is already available in the release candidate.

Thank you.

[mtelvers]

Related to #6007

[rjbou]

When we add a new binary target, it is only available for the ongoing release and future ones. We should add a note about that in the documentation.
We'll see if we can provide a riscv64 binary for 2.2.1, and more generally to provide the new binary target for last stable releases when they are added.

[kit-ty-kate]

This was fixed by #6293 with the release of 2.3.0