Migrated Tests from GitAPITestCase to GitAPITest

[GAyan17]

JENKINS-60940 - Migrate tests from JUnit 3 to JUnit 4

Migrated Tests from GitAPITestCase(JUnit 3) to GitAPITest(JUnit 4).
Tests Done are:

• testGetRemoteUrl
• testEmptyComment
• testCreateBranch
• testDeleteBranch
• testDeleteTag
• testListTagsWithFilter
• testListTagsWithoutFilter

Further more tests will eventually be migrated from JUnit 3 to JUnit 4.

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

Types of changes

• Infrastructure change (non-breaking change which updates dependencies or improves infrastructure)