Defang the lhash test

Defang the lhash test

This is bascially eating my mac, as it now runs for 80 seconds
and eats all the CPU's exercising lock contention.

This dials it back to consume at most a quarter of the CPU's in
use by HARNESS_JOBS, unless LHASH_WORKERS is set to override it
in which case we use that.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
(Merged from https://github.com/openssl/openssl/pull/29406)