test: migrate FileSystemFolderTest to junit 5

[MartinWitt]

#3919
The following has changed in the code:
Replaced junit 4 test annotation with junit 5 test annotation in jarFileIsNotSubfolder
Replaced junit 4 test annotation with junit 5 test annotation in testLauncherWithWrongPathAsInput
Transformed junit4 assert to junit 5 assertion in jarFileIsNotSubfolder
Transformed junit4 assert to junit 5 assertion in testLauncherWithWrongPathAsInput

[slarse]

Thanks @MartinWitt