feat: Build and release binaries for Linux RISC-V

[twz123]

Description, Motivation and Context

I'm currently evaluating k0s on RISC-V (k0sproject/k0s#1919). In case of test failures, the k0s integration tests use support-bundle to collect the cluster state for further investigation. It would be neat if there's a precompiled support-bundle binary available for RISC-V, so that troubleshooting integration test failures becomes a bit easier.

Things done:

• Add riscv64 to GOARCHes in .goreleaser.yaml
• Add riscv64/linux to goreleaser-test GitHub workflow job

Checklist

• New and existing tests pass locally with introduced changes.
• Tests for the changes have been added (for bug fixes / features)
• The commit message(s) are informative and highlight any breaking changes
• Any documentation required has been added/updated. For changes to https://troubleshoot.sh/ create a PR here

Does this PR introduce a breaking change?

• Yes
• No