ci: add ubuntu-24.04-riscv runner

[RoloEdits]

Adds support for testing and releasing RISC-V Linux.

The runners are provided by the RISE Project:

• https://riseproject.dev/2026/03/24/announcing-the-rise-risc-v-runners-free-native-risc-v-ci-on-github/
• https://riseproject-dev.github.io/riscv-runner/

To note, the runners' Ubuntu version is not coupled with the traditional full version offerings GitHub provides. This means that we have to use the 24.04 version, even though this could provide a GLIBC version that is newer than what users might have, and is also currently out of sync with the version we use for the other Linux releases for x86_64 and aarch64. Given that RISC-V is fairly new for desktop Linux, I think its fine to offer a best effort support here, as you could expect that most users would be on new kernels as support expands.

Considering that this is a 3rd party offering, this could be very slow to run. It might be worth it for releases, which are done rarely, but I'm also hesitant to offer a release build without also testing it.

RISC-V Linux is currently Tier: 2 (with Host Tools)

Closes: #15478

[RoloEdits]

This will need a member to act and install a github app for the organization: https://github.com/apps/rise-risc-v-runners