Several links in the reference manual still link to https://junit.org/junit5/ which no longer exists.

The JUnit site has redirects in place; however, we should simply link to
https://junit.org/.

Similarly, the JUnit documentation no longer resides at https://junit.org/junit5/docs/current/user-guide/ but rather at https://docs.junit.org/current/user-guide/.