Do not fail if ctx dup does not succeed

Do not fail if ctx dup does not succeed

If the ctx was *really* needed we'll probably fail later with an error
anyway, so no point in failing immediately.

Document that this behavior is dependent on the provider used to
implement the signature/verification.

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/20375)