Fix broken tests caused by replication

[b1ron]

In #633 the MongoDB service is now configured as a single node replica set, by default. We need to fix some assertions in the below examples to handle additional fields in the responses.

• https://github.com/FerretDB/java-example
• https://github.com/FerretDB/dotnet-example
• https://github.com/FerretDB/python-example