doc: improve assert docs

This improves the error example output by reflecting the current
state. It also makes sure the examples are up to date in general.
`assert.throws` clarified the `ERR_AMBIGUOUS_ARGUMENT` error.

PR-URL: https://github.com/nodejs/node/pull/20313


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>