Spring Security PowerMock is not compatible with Mockito 3.4.0

PowerMock maintains compatibility with Mockito 2.+ as stated in the PowerMock wiki https://github.com/powermock/powermock/wiki/mockito

We have previously used PowerMock with Mockito 3.3.+ without errors, however our build breaks with Mockito 3.4.0.

For now, we will restrict our Mockito dependency to 3.3.+. However, our goal is to remove the PowerMock dependency and upgrade to the latest version of Mockito. This is already tracked in gh-6025.