change string(model.metricnamelabel) to model.metricnamelabel (#8289)
change string(model.metricnamelabel) to model.metricnamelabel (#8289)

Signed-off-by: aSquare14 <3a8c23144fb74356cb50ab945c2410abe6c9f304@gmail.com>
alileza/prometheus,keegancsmith/prometheus,alileza/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,prometheus/prometheus,prometheus/prometheus,alileza/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus