Fix quic::GetPacketHeaderSize when QuicVersionHasLongHeaderLengths is false

gfe-relnote: Bugfix in quic::GetPacketHeaderSize protected by gfe2_reloadable_flag_quic_fix_get_packet_header_size
PiperOrigin-RevId: 256043642
Change-Id: I1f943400e15a684b5cb84f2a11cbb294859f669e
diff --git a/quic/core/quic_crypto_client_stream_test.cc b/quic/core/quic_crypto_client_stream_test.cc
index e0229bc..12fc9a2 100644
--- a/quic/core/quic_crypto_client_stream_test.cc
+++ b/quic/core/quic_crypto_client_stream_test.cc
@@ -315,6 +315,7 @@
 }
 
 TEST_F(QuicCryptoClientStreamTest, PreferredVersion) {
+  SetQuicReloadableFlag(quic_fix_get_packet_header_size, true);
   // This mimics the case where client receives version negotiation packet, such
   // that, the preferred version is different from the packets' version.
   connection_ = new PacketSavingConnection(