Please note that the named VT doesn’t work with anything like “trusted CA” and thus adding one wouldn’t prevent it from reporting.
Instead it works on a fixed list of issuer names of a certificate defined in the if( check_for == "untrusted_ca" ) { part of ssl_func.inc and reports accordingly.
The reason is if one of such issue names are in use there is usually something really “fishy” going on on the target / connection which requires a closer look.