Add riscv64 runners

Author: yuzibo

.github/workflows/ci.yml

@@ -102,6 +102,7 @@ jobs:
           - ubuntu-24.04-arm
           - macos-latest
           - windows-latest
+          - [self-hosted, linux, riscv64]
         # 1.91 is the MSRV
         rust-version: ["1.91", stable]
       fail-fast: false