Use proto.Marshal instead of calling Marshal() on objects

With google.golang.org/protobuf, proto-generated objects only have
ProtoReflect(). They don't have Marshal() anymore (see #6564).

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

services/tasks/local.go

@@ -42,6 +42,7 @@ import (
 	"github.com/containerd/containerd/pkg/timeout"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/protobuf"
+	"github.com/containerd/containerd/protobuf/proto"
 	ptypes "github.com/containerd/containerd/protobuf/types"
 	"github.com/containerd/containerd/runtime"
 	"github.com/containerd/containerd/runtime/linux/runctypes"
@@ -579,7 +580,8 @@ func (l *local) Checkpoint(ctx context.Context, r *api.CheckpointTaskRequest, _
 		return nil, err
 	}
 	// write the config to the content store
-	data, err := protobuf.FromAny(container.Spec).Marshal()
+	pbany := protobuf.FromAny(container.Spec)
+	data, err := proto.Marshal(pbany)
 	if err != nil {
 		return nil, err
 	}