report: add missing locks for report_on_fatalerror accessors

Overlooked in 2fa74e3e.

Refs: https://github.com/nodejs/node/pull/32207

PR-URL: https://github.com/nodejs/node/pull/32535


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>