Update WebTransport header names.

https://github.com/ietf-wg-webtrans/draft-ietf-webtrans-http3/commit/b2dce6ac103b83ae28e6164bf251ad841a6cbe43

PiperOrigin-RevId: 680737394

quiche/web_transport/web_transport_headers.h

diff --git a/quiche/web_transport/web_transport_headers.h b/quiche/web_transport/web_transport_headers.h
index 6cf16ee..c43fcf3 100644
--- a/quiche/web_transport/web_transport_headers.h
+++ b/quiche/web_transport/web_transport_headers.h
@@ -17,9 +17,8 @@
 namespace webtransport {
 
 inline constexpr absl::string_view kSubprotocolRequestHeader =
-    "WebTransport-Subprotocols-Available";
-inline constexpr absl::string_view kSubprotocolResponseHeader =
-    "WebTransport-Subprotocol";
+    "WT-Available-Protocols";
+inline constexpr absl::string_view kSubprotocolResponseHeader = "WT-Protocol";
 
 QUICHE_EXPORT absl::StatusOr<std::vector<std::string>>
 ParseSubprotocolRequestHeader(absl::string_view value);