Fix buffer overflow issue by changing how test string is created.

gfe-relnote: n/a. test only.
PiperOrigin-RevId: 275954569
Change-Id: I01c313eac723e643879602c768bda05575f46ae0

quic/core/quic_packet_creator_test.cc

diff --git a/quic/core/quic_packet_creator_test.cc b/quic/core/quic_packet_creator_test.cc
index 4fe07ad..b7ced21 100644
--- a/quic/core/quic_packet_creator_test.cc
+++ b/quic/core/quic_packet_creator_test.cc
@@ -2395,7 +2395,7 @@
 
   // frame is for another stream, so it won't be coalesced.
   const auto length = creator_.BytesFree() - 10u;
-  std::string large_data("x", length);
+  std::string large_data(length, 'x');
   MakeIOVector(large_data, &iov_);
   EXPECT_CALL(debug, OnFrameAddedToPacket(_));
   ASSERT_TRUE(creator_.ConsumeDataToFillCurrentPacket(