zmlocalconfig -e data_source_trust_self_signed_certs = true
(Or import into the keystore if it's a one time thing.)
Bug 35441 - external data sources with self-signed/expired certs no longer work requesting a bypass prompt / data_source_trust_self_signed_certs_override_ allowed attribute (or we could re-use ssl_allow_accept_untrusted_certs) was closed as wontfix (I tried - your welcome to comment / vote for it) in favor of
Bug 35892 - clean up error dialog for external data sources (just cleanup to fit / making that a better error message such as: "Self-signed or mismatched certs are currently not allowed - please contact your admin for further options").