Make weld-testing version 5.x compatible with JUnit 6

[manovotn]

Originated from issue #293

JUnit 6 has been released and we have some minor incompatibilities to deal with in order to run with it.
We can easily adjust our code to be able to execute with both, JUnit 5 and JUnit 6 although we want to keep the baseline version 5 for the time being. Reasons for that are not breaking existing usage which might be using other JUnit 5 extensions with possible compatibility issues and Spock will not work with JUnit 6 from what I understood.

Users will therefore be able to manually specify JUnit 6 if they so wish.

[otaviojava]

Thank you, @manovotn. When I moved to Jupiter 6.0.0, my tests broke, I returned to the previous version (5.14.0).

[manovotn]

@otaviojava there should be a 5.0.3.Final release available about now which will allow you to use JUnit 6 is you so wish :)

[otaviojava]

Thank you @manovotn