Migrating tests of GitAPITestCase from JUnit 3 to JUnit 4

[GAyan17]

JENKINS-60940 - Migrating tests of GitAPITestCase from JUnit 3 to JUnit 4

In this PR, the test migrated is:

• testCleanWithParameters
• testClean
• testHasGitRepo

Describe the big picture of your changes here to explain to the maintainers why this pull request should be accepted.
If it fixes a bug or resolves a feature request, include a link to the issue.

Checklist

• I have read the CONTRIBUTING doc
• I have referenced the Jira issue related to my changes in one or more commit messages
• I have added tests that verify my changes
• Unit tests pass locally with my changes
• I have added documentation as necessary
• No Javadoc warnings were introduced with my changes
• No spotbugs warnings were introduced with my changes
• I have interactively tested my changes

Types of changes

What types of changes does your code introduce?

• Tests

[MarkEWaite]

Needs to have the changes reverted that are purely white space. White space changes make other pull requests have unnecessary conflicts. See the CONTRIBUTING file for more details describing why this plugin needs to leave its ugly formatting alone.

[GAyan17]

Thanks @MarkEWaite for the code suggestion review, I will surely keep that in mind for other pull requests.