Updates the `QUIC_STREAM_EXCESSIVE_LOAD` code comments to reflect broader usage.

See https://github.com/envoyproxy/envoy/pull/39007 for a new Envoy usage of the error code.

PiperOrigin-RevId: 743655095

quiche/quic/core/quic_error_codes.h

diff --git a/quiche/quic/core/quic_error_codes.h b/quiche/quic/core/quic_error_codes.h
index d37da04..64a3fbb 100644
--- a/quiche/quic/core/quic_error_codes.h
+++ b/quiche/quic/core/quic_error_codes.h
@@ -75,7 +75,7 @@
   // A frame that fails to satisfy layout requirements or with an invalid size
   // was received.
   QUIC_STREAM_FRAME_ERROR = 23,
-  // Peer exhibits a behavior that might be generating excessive load.
+  // The system is experiencing excessive load, possibly due to peer behavior.
   QUIC_STREAM_EXCESSIVE_LOAD = 24,
   // A Stream ID or Push ID was used incorrectly, such as exceeding a limit,
   // reducing a limit, or being reused.