Fix "non-constant-expression cannot be narrowed from type 'uint8_t' (aka 'unsigned char') to 'char' in initializer list [-Wc++11-narrowing]" in chromium build.

PiperOrigin-RevId: 478061642

quiche/binary_http/binary_http_message_test.cc

diff --git a/quiche/binary_http/binary_http_message_test.cc b/quiche/binary_http/binary_http_message_test.cc
index 67a1326..dc6b279 100644
--- a/quiche/binary_http/binary_http_message_test.cc
+++ b/quiche/binary_http/binary_http_message_test.cc
@@ -16,9 +16,9 @@
 namespace {
 
 std::string WordToBytes(uint32_t word) {
-  return std::string(
-      {static_cast<uint8_t>(word >> 24), static_cast<uint8_t>(word >> 16),
-       static_cast<uint8_t>(word >> 8), static_cast<uint8_t>(word)});
+  return std::string({static_cast<char>(word >> 24),
+                      static_cast<char>(word >> 16),
+                      static_cast<char>(word >> 8), static_cast<char>(word)});
 }
 
 template <class T>