Fix unit test

Author: sunnylovestiramisu

pkg/gce-pd-csi-driver/controller_test.go

@@ -798,7 +798,7 @@ func TestCreateVolumeArguments(t *testing.T) {
 				Name:               name,
 				CapacityRange:      stdCapRange,
 				VolumeCapabilities: stdVolCaps,
-				Parameters:         map[string]string{"labels": "key1=value1,key2=value2", "provisioned-iops-on-create": 10000},
+				Parameters:         map[string]string{"labels": "key1=value1,key2=value2", "provisioned-iops-on-create": "10000"},
 			},
 			expVol: &csi.Volume{
 				CapacityBytes:      common.GbToBytes(20),