Set WebTransport unidirectional stream to use level-triggered read notifications.

The existing code assumes they already operate in that mode.

PiperOrigin-RevId: 479095236

quiche/quic/core/http/web_transport_http3.cc

diff --git a/quiche/quic/core/http/web_transport_http3.cc b/quiche/quic/core/http/web_transport_http3.cc
index 888331e..84f1d33 100644
--- a/quiche/quic/core/http/web_transport_http3.cc
+++ b/quiche/quic/core/http/web_transport_http3.cc
@@ -300,7 +300,9 @@
     : QuicStream(pending, session, /*is_static=*/false),
       session_(session),
       adapter_(session, this, sequencer()),
-      needs_to_send_preamble_(false) {}
+      needs_to_send_preamble_(false) {
+  sequencer()->set_level_triggered(true);
+}
 
 WebTransportHttp3UnidirectionalStream::WebTransportHttp3UnidirectionalStream(
     QuicStreamId id, QuicSpdySession* session, WebTransportSessionId session_id)