80-test_cms.t: Add test case for verification of multiple signatures

80-test_cms.t: Add test case for verification of multiple signatures

openssl cms -verify requires all signatures to pass verification, so adding
a signature with -resign will cause overall verification to fail if the new
signature cannot be verified.

As I intend to optionally allow this case (see #26382), this new test
case ensures that the current behaviour stays the default.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/27269)