Add riscv64 architecture support

[gounthar]

actions/setup-python fails on riscv64 runners because actions/python-versions does not provide pre-built Python binaries for linux/riscv64:

Error: The version '3.11 - 3.14' with architecture 'riscv64' was not found for Ubuntu 24.04.

This blocks all Python CI workflows on riscv64 GitHub Actions runners. RISC-V self-hosted runners are becoming available through the RISE RISC-V runners program, used by projects like numpy, llama.cpp, and pytorch.

CPython supports riscv64 as a Tier 3 platform and builds natively on current hardware.

Ideally, actions/python-versions would add riscv64 to its build matrix. As a shorter-term fix, setup-python could fall back to system Python when pre-built binaries are unavailable for the current architecture.

[chiranjib-swain]

Hi @gounthar, thanks for raising this. We’ll review it and get back to you once we have feedback.