This is the same as MDEV-35368, which was previously incompletely fixed
(on *nix-only, for unix socket connections)
This time, we fix it compatibly to Connector/C, by not verifying
server certificate for local connections, which, in addition to socket
and named pipe, are also "127.0.0.1" and "::1", and on Windows "localhost"
as well.
The corresponding code in Connector/C is was added by
1287c901dc8515823d28edcebfe4be65e6c5a6b3.
It remain a good question whether mariabackup should use SSL at all
since all it does are local connections, for "BACKUP STAGE" stuff.