test: fix postmortem metadata test

Recent changes to spawnSync (nodejs#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.

Author: mmarchini

test/v8-updates/test-postmortem-metadata.js

@@ -21,7 +21,7 @@ if (common.isAIX)
 if (common.isOpenBSD)
   common.skip('no v8 debug symbols on OpenBSD');
 
-const nm = spawnSync('nm', args);
+const nm = spawnSync('nm', args, { maxBuffer: Infinity });
 
 if (nm.error && nm.error.errno === 'ENOENT')
   common.skip('nm not found on system');