Update client to store groupKey under TaskMessage

client.go

@@ -375,6 +375,7 @@ func (c *Client) EnqueueContext(ctx context.Context, task *Task, opts ...Option)
 		Deadline:  deadline.Unix(),
 		Timeout:   int64(timeout.Seconds()),
 		UniqueKey: uniqueKey,
+		GroupKey:  opt.groupKey,
 		Retention: int64(opt.retention.Seconds()),
 	}
 	now := time.Now()

client_test.go

@@ -528,6 +528,7 @@ func TestClientEnqueueWithGroupOption(t *testing.T) {
 								Queue:    "default",
 								Timeout:  int64(defaultTimeout.Seconds()),
 								Deadline: noDeadline.Unix(),
+								GroupKey: "mygroup",
 							},
 							Score: now.Unix(),
 						},
@@ -576,6 +577,7 @@ func TestClientEnqueueWithGroupOption(t *testing.T) {
 							Queue:    "default",
 							Timeout:  int64(defaultTimeout.Seconds()),
 							Deadline: noDeadline.Unix(),
+							GroupKey: "mygroup",
 						},
 						Score: now.Add(30 * time.Minute).Unix(),
 					},