Incorrect anchor in docs for listeners

[rasjani]

That links just leads to the top of the docs.

Actual link in the page is: https://robotframework.org/robotframework/latest/RobotFrameworkUserGuide.html#listener-interface-methods

And there was also a comment:

These docs should also be updated to mention that listener v3 is the default since RF 7.0 (https://github.com/robotframework/robotframework/issues/4910).