tests: adjust config_test for db::string_map changes
tests: adjust config_test for db::string_map changes

scylladb/scylla,kjniemi/scylla,avikivity/scylla,avikivity/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla,raphaelsc/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,kjniemi/scylla,raphaelsc/scylla,duarten/scylla