[windows] Fix forward for CBF in artifact build (#30886)

* fix

* Update tchar.cc

src/core/lib/gprpp/tchar.cc

@@ -25,7 +25,8 @@ TcharString CharToTchar(std::string input) {
   int needed = MultiByteToWideChar(CP_UTF8, 0, input.c_str(), -1, NULL, 0);
   if (needed <= 0) return TcharString();
   TcharString ret(needed, L'\0');
-  MultiByteToWideChar(CP_UTF8, 0, input.c_str(), -1, ret.c_str(), needed);
+  MultiByteToWideChar(CP_UTF8, 0, input.c_str(), -1,
+                      const_cast<LPTSTR>(ret.data()), needed);
   return ret;
 }
 
@@ -34,8 +35,8 @@ std::string TcharToChar(TcharString input) {
       WideCharToMultiByte(CP_UTF8, 0, input.c_str(), -1, NULL, 0, NULL, NULL);
   if (needed <= 0) return std::string();
   std::string ret(needed, '\0');
-  WideCharToMultiByte(CP_UTF8, 0, input.c_str(), -1, ret.c_str(), needed, NULL,
-                      NULL);
+  WideCharToMultiByte(CP_UTF8, 0, input.c_str(), -1,
+                      const_cast<LPSTR>(ret.data()), needed, NULL, NULL);
   return ret;
 }
 #else