doc: fix EventEmitter#eventNames() example

Checklist

• documentation is changed or added
• the commit message follows commit guidelines

Affected core subsystem(s)

doc

Description of change

Replace myErr with myEE in one place (that was obviously a mistype). Fix the expected output to have the actual formatting.

This was overlooked in #5617 (I also didn't notice that).

/cc @jasnell