Add a unit test to validate the functionality of our reg key lookups

Add a unit test to validate the functionality of our reg key lookups

Add a test to check to make sure our registry key lookups work.  note
this test only runs on windows (clearly), but also only if the registry
keys are set via an installer or some other manual process (to be done
in the CI workflow)

Also add workflow steps to set registry keys for testing

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24450)