test: fix warning in test_environment.cc

```
warning log:
../test/cctest/test_environment.cc: In constructor   \
‘RedirectStdErr::RedirectStdErr(const char*)’:
../test/cctest/test_environment.cc:77:12: warning:   \
ignoring return value of ‘FILE* freopen(const char*, \
const char*, FILE*)’, declared with attribute
warn_unused_result [-Wunused-result]
     freopen(filename_, "w", stderr);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
```

PR-URL: https://github.com/nodejs/node/pull/36846


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>