Failing test in CI: caused by Mocha's new unhandledRejection listener

[freelerobot]

1. error-reporting
   "before all" hook for "Should correctly publish an error that is an Error object":

   AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:

1 !== 0

  + expected - actual

  -1
  +0
  
  at Context.<anonymous> (build/system-test/error-reporting.js:342:16)
      -> /workspace/system-test/error-reporting.ts:447:12
  at processImmediate (internal/timers.js:456:21)

Cause: Last week Mocha 15 added a default listener on the unhandledRejection event. See mochajs/mocha/issues/2640

(reason, promise) => {
      if (isMochaError(reason)) {
        debug(
          'trapped unhandled rejection coming out of Mocha; forwarding to uncaught handler:',
          reason
        );
        this.uncaught(reason);
      } else {
        debug(
          'trapped unhandled rejection from (probably) user code; re-emitting on process'
        );
        this._removeEventListener(
          process,
          'unhandledRejection',
          this.unhandled
        );
        try {
          process.emit('unhandledRejection', reason, promise);
        } finally {
          this._addEventListener(process, 'unhandledRejection', this.unhandled);
        }
      }
    }