Cleanup: Replace deprecated `unittest.assertEquals` with `assertEqual`

[Vaishnav88sk]

What should be cleaned up or changed:
The tests in gubernator/view_pr_test.py are using self.assertEquals(). The assertEquals method has been deprecated in Python's unittest module since Python 3.2. We should pay down this technical debt and use self.assertEqual() instead to avoid deprecation warnings and ensure long-term compatibility.

Provide any links for context:
The deprecated method is currently used in these locations:

• https://github.com/kubernetes/test-infra/blob/master/gubernator/view_pr_test.py#L37
• https://github.com/kubernetes/test-infra/blob/master/gubernator/view_pr_test.py#L38
• https://github.com/kubernetes/test-infra/blob/master/gubernator/view_pr_test.py#L50

[Vaishnav88sk]

/sig testing

[Vaishnav88sk]

/assign