Regression test for dependency convergence problem fixed in 3.0.0

About 5 years ago, I reported a dependency convergence issue (back then for 1.4.1), but accidentally in the Extra Enforcer Rules bug tracker where it was simply forgotten or ignored despite a reproducing test case:

https://github.com/mojohaus/extra-enforcer-rules/issues/28

Back then, neither I nor any committer noticed that I had posted in the wrong bug tracker. Had anybody even so much as taken a closer look, this would have been noticed. In the meantime, the bug still existed until and including 3.0.0-M3 and was only recently fixed for 3.0.0 in commit ca40308f as a side-effect of upgrading maven-dependency-tree.

Because slachiewicz told me that new integration tests shielding the plugin from regression bugs are welcome, I am going to create a PR containing the corresponding IT. I already verified that it fails as expected before commit ca40308f and passes afterwards. So if for whatever reason the problem resurfaces, the IT will catch it. It also documents that there actually was a problem which was fixed rather accidentally by upgrading a dependency.