hostinger: fix record update

[ldez]

The API documentation is not clear.

Update DNS records for the selected domain.

Using overwrite = true will replace existing records with the provided ones. Otherwise, existing records will be updated and new records will be added.

The update of the recordsets uses name/subdomain + type as a "key".

When using overwrite = false, the update only applies to the recordset explicitly defined inside the request body based on the "key" and not against the zone as a whole.

And if one of the updated records, inside a recordset, already exists, a cryptic error is thrown:

[DNS:4008] DNS resource record is not valid or conflicts with another resource record

Fixes #2688