Add native riscv64 CI using RISE RISC-V GitHub Actions Runners

Background

The RISE Project (a Linux Foundation initiative dedicated to accelerating the RISC-V software ecosystem) has announced RISE RISC-V Runners: a free, managed GitHub Actions runner service that gives any open source project access to real RISC-V hardware in their CI pipeline. https://riseproject.dev/2026/03/24/announcing-the-rise-risc-v-runners-free-native-risc-v-ci-on-github/

Proposed changes install the RISE RISC-V Runners GitHub App on the k3s-io organization.