test: show child stderr output in largepages test

The test starts child processes. A recent change is suspected of causing
flaky crashes on one of the alpine buildbots but we can't know for sure
because the test hides the child's stderr.
Refs: #31547 (comment)
PR-URL: #31612
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: bnoordhuis

test/parallel/test-startup-large-pages.js

@@ -8,7 +8,8 @@ const { spawnSync } = require('child_process');
 
 {
 constchild=spawnSync(process.execPath,
-['--use-largepages=on','-p','42']);
+['--use-largepages=on','-p','42'],
+{stdio: ['inherit','pipe','inherit']});
 conststdout=child.stdout.toString().match(/\S+/g);
 assert.strictEqual(child.status,0);
 assert.strictEqual(child.signal,null);