test: fix postmortem metadata test

Recent changes to spawnSync (https://github.com/nodejs/node/pull/23027)
broke our V8 postmortem tests since the output from nm was larger than
the new default maxBuffer for spawnSync. Changing the maxBuffer to
Infinity fixes the issue.

PR-URL: https://github.com/nodejs/node/pull/27265
Refs: https://github.com/v8/v8/compare/7.4.288.18...7.4.288.21


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>