ptrace_single_step currently returns EOPNOTSUPP on riscv.
This temporarily fixes the following CI failures:
https://ci.freebsd.org/job/FreeBSD-main-riscv64-test/16606/testReport/sys.kern/ptrace_test/ptrace__PT_STEP_with_signal/
https://ci.freebsd.org/job/FreeBSD-main-riscv64-test/16606/testReport/sys.kern/ptrace_test/ptrace__step_siginfo/