RRset duplicates are taken into account not to confuse dns-api

[bazilek]

Should fix for the following case:

Renewing an existing certificate for *.preprod.be
Unsafe permissions on credentials configuration file: ./creds
Error. PUT: 'https://api.preprod.world/dns/v2/zones/preprod.be/_acme-challenge.preprod.be/TXT', data: "{'resource_records': [{'content': ['xTykygpQ7cFLC_t7MbU1UP6DdH5-D2xTrwRK40STEYY'], 'enabled': True}, {'content': ['xTykygpQ7cFLC_t7MbU1UP6DdH5-D2xTrwRK40STEYY'], 'enabled': True}], 'ttl': 300}", response: {"error":"two or more records have same content"}

Failed to renew certificate preprod.be with error: {"error":"two or more records have same content"}