fixup! fs: add c++ fast path for writeFileSync utf8

Author: CanadaHonk

benchmark/fs/bench-writeFileSync.js

@@ -14,6 +14,7 @@ const bench = common.createBenchmark(main, {
 });
 
 function main({ n, encoding, stringLength, hasFileDescriptor }) {
+  tmpdir.refresh();
   const enc = encoding === 'undefined' ? undefined : encoding;
   const path = tmpdir.resolve(`.writefilesync-file-${Date.now()}`);