assert: fix actual & expected input

This makes sure the actual and expected values on the error thrown
by `assert.throws` etc. are always as they should be.

PR-URL: https://github.com/nodejs/node/pull/19925


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>