test: add required settings to test-benchmark-buffer

A benchmark was added but the appropriate settings were not added to
test-benchmark-buffer. These two additions make sure that the new
benchmark file only runs a single benchmark during testing.

PR-URL: #29163
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

test/benchmark/test-benchmark-buffer.js

@@ -9,6 +9,7 @@ runBenchmark('buffers',
                'aligned=true',
                'args=1',
                'buffer=fast',
+               'bytes=0',
                'byteLength=1',
                'charsPerLine=6',
                'encoding=utf8',
@@ -17,6 +18,7 @@ runBenchmark('buffers',
                'linesCount=1',
                'method=',
                'n=1',
+               'partial=true',
                'pieces=1',
                'pieceSize=1',
                'search=@',