test: simplify for loop in test-buffer-zero-fill-cli.js

PR-URL: #26799
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

test/parallel/test-buffer-zero-fill-cli.js

@@ -9,8 +9,8 @@ const SlowBuffer = require('buffer').SlowBuffer;
 const assert = require('assert');
 
 function isZeroFilled(buf) {
-  for (let n = 0; n < buf.length; n++)
-    if (buf[n] > 0) return false;
+  for (const n of buf)
+    if (n > 0) return false;
   return true;
 }