test: fix test-benchmark-buffer

Using `len=2` in test-benchmark-buffer was resulting in a `RangeError` in buffer-base64-encode.js. Change to `len=256` which works in all buffer benchmarks. PR-URL: nodejs#27260 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Luigi Pinca <luigipinca@gmail.com> Reviewed-By: Refael Ackermann <refack@gmail.com>

Author: Trott

test/benchmark/test-benchmark-buffer.js

@@ -13,7 +13,7 @@ runBenchmark('buffers',
  'charsPerLine=6',
  'encoding=utf8',
  'endian=BE',
- 'len=2',
+ 'len=256',
  'linesCount=1',
  'method=',
  'n=1',