fix typo of flag name (#29154)

paddle/fluid/platform/enforce.h

@@ -284,8 +284,8 @@ inline std::string GetErrorSumaryString(StrType&& what, const char* file,
     // NOTE(chenweihang): if no C++ backtrace, give a hint to tell users
     // how to show C++ backtrace, this hint only show in 2.0-rc verison,
     // and will be removed in 2.0 official version
-    sout << "\n  [Hint: If need to show C++ stacktraces, please set "
-            "`FlAGS_call_stack_level=2`.]";
+    sout << "\n  [Hint: If you need C++ stacktraces for debugging, please set "
+            "`FLAGS_call_stack_level=2`.]";
   }
   sout << std::endl;
   return sout.str();