test: add arg to narrow http benchmark test

PR-URL: https://github.com/nodejs/node/pull/26101
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/benchmark/test-benchmark-http.js

@@ -29,7 +29,8 @@ runBenchmark('http',
                'n=1',
                'res=normal',
                'type=asc',
-               'value=X-Powered-By'
+               'value=X-Powered-By',
+               'headerDuplicates=1',
              ],
              {
                NODEJS_BENCHMARK_ZERO_ALLOWED: 1,