CI: Pin riscv-compliance repo to specific commit
CI: Pin riscv-compliance repo to specific commit

Recently changes in the RISC-V compliance repo have caused our tests to
fail. That indicent highlighted the issue that we use the latest master
version of the compliance suite without pinning the version.

This PR fixes that by pinning to a specific version where our tests
still succeeded.

Upstream PR to fix actual failure: https://github.com/riscv/riscv-compliance/pull/92
Works around #608

lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex