test: reversed params in assert.strictEqual()

Reversed parameters of assert.strictEqual() in
test-promises-unhandled-rejections.js so that first one is actual and
second one is expected value.

PR-URL: https://github.com/nodejs/node/pull/23591


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>