acl: call stop for the upgrade goroutine when done

TestAgentLeaks_Server was reporting a goroutine leak without this. Not sure if it would actually
be a leak in production or if this is due to the test setup, but seems easy enough to call it
this way until we remove legacyACLTokenUpgrade.

agent/consul/leader.go

@@ -569,6 +569,7 @@ func (s *Server) legacyACLTokenUpgrade(ctx context.Context) error {
 
 		if len(tokens) == 0 {
 			// No new legacy tokens can be created, so we can exit
+			s.stopACLUpgrade() // required to prevent goroutine leak, according to TestAgentLeaks_Server
 			return nil
 		}
 

agent/routine-leak-checker/leak_test.go

@@ -6,12 +6,13 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/stretchr/testify/require"
+	"go.uber.org/goleak"
+
 	"github.com/hashicorp/consul/agent"
 	"github.com/hashicorp/consul/sdk/testutil"
 	"github.com/hashicorp/consul/testrpc"
 	"github.com/hashicorp/consul/tlsutil"
-	"github.com/stretchr/testify/require"
-	"go.uber.org/goleak"
 )
 
 func testTLSCertificates(serverName string) (cert string, key string, cacert string, err error) {