Update ErrorProne to the latest version

Over the past year (?) we have received Dependabot updates for ErrorProne. However, they fail the pipeline as the newest versions of ErrorProne catch existing issues in the codebase. An example PR from Dependabot: https://github.com/mockito/mockito/pull/3488

We need to update our version, as well as fix the pre-existing issues it catches. This is a good first issue to pick up, as it only requires compilation to succeed on the latest ErrorProne version.