tests: Fix the sync_cmd_get_more test
tests: Fix the sync_cmd_get_more test

mongo_sync_cmd_get_more() must be called with a namespace, not just a
database, so use config.ns.

Signed-off-by: Gergely Nagy <6780fac3b38619ac20422286e4110a70dbba2203@balabit.hu>

algernon/libmongo-client,algernon/libmongo-client,algernon/libmongo-client