Bump mockito-core from 2.27.0 to 2.28.1

Bumps [mockito-core](https://github.com/mockito/mockito) from 2.27.0 to 2.28.1.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](https://github.com/mockito/mockito/compare/v2.27.0...v2.28.1)