Bump deps/riscv-coq from 8587bd4 to a1f9454

Bumps [deps/riscv-coq](https://github.com/mit-plv/riscv-coq) from `8587bd4` to `a1f9454`.
- [Release notes](https://github.com/mit-plv/riscv-coq/releases)
- [Commits](mit-plv/riscv-coq@8587bd4...a1f9454)

---
updated-dependencies:
- dependency-name: deps/riscv-coq
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>