Fix links to JUnit User Guide
Overview
Since the JUnit User Guide is now based on Antora, our links to JUnit's user guide are now broken. Well, actually they simply all redirect to the overview page of the user guide.
For example, https://docs.junit.org/current/user-guide/#running-tests-config-params redirects to https://docs.junit.org/6.0.2/overview.html#running-tests-config-params, which is the overview.html page, and the #running-tests-config-params anchor is no longer applicable.
Whereas, for the particular link, we'll now need to use https://docs.junit.org/current/running-tests/configuration-parameters.html