Starting from 7.0 SERVER-74567 it is possible to shard collections in `admin` database.
Before 7.0 the shardCollection operation for `admin` collections were directed to the config server, and they were failing with NoShardingEnabled because _shardsvrCreateCollection command was performing this check that was failing on the config server.
Since SERVER-74567 this check is passing on the config server that now has both configsvr and shardsvr roles.