fix: data race in gRPC client trailer

pkg/remote/trans/nphttp2/grpc/http2_client.go

@@ -553,7 +553,9 @@ func (t *http2Client) closeStream(s *Stream, err error, rst bool, rstCode http2.
 	// only after updating this.
 	s.status = st
 	if len(mdata) > 0 {
+		s.cliTlrMu.Lock()
 		s.trailer = mdata
+		s.cliTlrMu.Unlock()
 	}
 	if err != nil {
 		// This will unblock reads eventually.

pkg/remote/trans/nphttp2/grpc/transport.go

@@ -260,6 +260,9 @@ type Stream struct {
 
 	// hdrMu protects header and trailer metadata on the server-side.
 	hdrMu sync.Mutex
+	// cliTlrMu protects trailer metadata on the client-side
+	cliTlrMu sync.RWMutex
+
 	// On client side, header keeps the received header metadata.
 	//
 	// On server side, header keeps the header set by SetHeader(). The complete
@@ -388,7 +391,9 @@ func (s *Stream) TrailersOnly() bool {
 // It can be safely read only after stream has ended that is either read
 // or write have returned io.EOF.
 func (s *Stream) Trailer() metadata.MD {
+	s.cliTlrMu.RLock()
 	c := s.trailer.Copy()
+	s.cliTlrMu.RUnlock()
 	return c
 }