benchmark: fix http elapsed time

Since commit 4e9ad206, elapsed time is expected to be a BigInt
instead of an array.

Refs: https://github.com/nodejs/node/pull/38369

PR-URL: https://github.com/nodejs/node/pull/38743


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>