test: upgrade test suite to use latest JUnit version

[algomaster99]

I need to upgrade in order to write good tests. I could use https://github.com/MartinWitt/laughing-train for this problem, but I was not able to build it on my system :/

The refactoring was pretty straightforward. I changed import statements, Ignore is now called Disabled, and reason argument is not the last - after expected and actual.

[algomaster99]

This PR is a reminder that even the simplest of problems can take a bit of your time 😢

The only test that fails it is because of a diff UPDATE: TestCase to junit.framework.TestCase. In the left version, TestCase is imported using wildcard and in the right version, TestCase is imported using its fully qualified name.

With JUnit4 in the classpath, gumtree-spoon resolves that TestCase is same as junit.framework.TestCase since junit.framework,TestCase is an API from JUnit4. However, when we update the JUnit version, spoon model cannot infer the same. If we also include junit.junit:4.13.2, the problem goes away, but I don't want to have dependencies to test resources in pom.xml.

@MartinWitt @I-Al-Istannen, did you see such a bug when porting JUnit 4 to JUnit 5 in spoon?