Use GetGuaranteedLargestMessagePayload in SendMessages to make it less flaky. GetCurrentLargestMessagePayload maybe 1-byte larger when there is pending frames, and this will be addressed in b/155761918.

PiperOrigin-RevId: 310159563
Change-Id: I49ffc55159a787781040776222f3caf77d198619
diff --git a/quic/core/http/end_to_end_test.cc b/quic/core/http/end_to_end_test.cc
index af52b12..ccbe3af 100644
--- a/quic/core/http/end_to_end_test.cc
+++ b/quic/core/http/end_to_end_test.cc
@@ -3809,7 +3809,7 @@
     for (size_t i = 2; i <= kTestMaxNumberOfMessages; ++i) {
       size_t message_length =
           random->RandUint64() %
-              client_session->GetCurrentLargestMessagePayload() +
+              client_session->GetGuaranteedLargestMessagePayload() +
           1;
       MessageResult result = client_session->SendMessage(MakeSpan(
           client_session->connection()