RedisCache() without arguments fails at construction with
"ValueError: Either 'host' or 'url' must be specified for redis."
The actual Redis connection is irrelevant since async_set_cache is mocked.
Unlike test_get_team_redis which uses client_no_auth (which sets REDIS_HOST
via fake_env_vars), test_team_update_redis has no fixture setting that env var.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>