test: cover stdout/stderr usage in triggerReport()

This commit adds coverage for the cases where
process.report.filename is 'stdout' or 'stderr'.

PR-URL: https://github.com/nodejs/node/pull/26522


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>