test: migrate SourcePositionTest to JUnit 5

[MartinWitt]

#3919
The following has changed in the code:
Replaced junit 4 test annotation with junit 5 test annotation in testSourcePosition
Replaced junit 4 test annotation with junit 5 test annotation in test_sourcePositionOfTypeInFieldExists
Replaced junit 4 test annotation with junit 5 test annotation in equalPositionsHaveSameHashcode
Replaced junit 4 test annotation with junit 5 test annotation in testSourcePositionOfSecondPrimitiveType
Replaced junit 4 test annotation with junit 5 test annotation in testSourcePositionStringFragment
Replaced junit 4 test annotation with junit 5 test annotation in testSourcePositionWhenCommentInAnnotation
Transformed junit4 assert to junit 5 assertion in testSourcePosition
Transformed junit4 assert to junit 5 assertion in test_sourcePositionOfTypeInFieldExists
Transformed junit4 assert to junit 5 assertion in equalPositionsHaveSameHashcode
Transformed junit4 assert to junit 5 assertion in testSourcePositionOfSecondPrimitiveType
Transformed junit4 assert to junit 5 assertion in testSourcePositionStringFragment
Transformed junit4 assert to junit 5 assertion in testSourcePositionWhenCommentInAnnotation

[MartinWitt]

@tiulpin here is another failing qodana run
Edit: Link because we need a rerun: https://github.com/INRIA/spoon/runs/4761985160?check_suite_focus=true