chore: migrate from unmaintained mockgen (#11547)

The golang mock package has been archived and is now maintained by uber.

> Update, June 2023: This repo and tool are no longer maintained. Please
> see go.uber.org/mock for a maintained fork instead.

[1] https://github.com/golang/mock
[2] https://github.com/uber-go/mock

core/wrapper/chargemeter_test.go

@@ -3,7 +3,7 @@ package wrapper
 import (
 	"testing"
 
-	"github.com/golang/mock/gomock"
+	"go.uber.org/mock/gomock"
 )
 
 func TestProxyChargeMeter(t *testing.T) {

core/wrapper/chargerater_test.go

@@ -7,7 +7,7 @@ import (
 	"github.com/benbjohnson/clock"
 	"github.com/evcc-io/evcc/api"
 	"github.com/evcc-io/evcc/util"
-	"github.com/golang/mock/gomock"
+	"go.uber.org/mock/gomock"
 )
 
 func TestNoMeter(t *testing.T) {