Fix build with gcc12

Fixes the following error:
   ```
   error: loop variable ‘json_in’ of type ‘const std::string&’ {aka
   ‘const std::__cxx11::basic_string<char>&’} binds to a temporary
   constructed from type ‘const char* const’
   ```

This patch has been applied to V8 in a separate CL:
https://crrev.com/c/5440536
Adding the fix here for future pulls.

Change-Id: I263f8fee76d2b3b432c50cb43c9fd68f75148b94
2 files changed