[UnusedVariable] Add MockitoBean in exempting variable annotations

[alexandrenavarro]

[UnusedVariable] Add MockitoBean in EXEMPTING_VARIABLE_ANNOTATIONS for UnusedVariable because spring 6.2 is migrating from MockBean to MockitoBean.

See spring 6.2 documentation https://docs.spring.io/spring-boot/api/java/org/springframework/boot/test/mock/mockito/MockBean.html

Don't hesitate if you have any questions / comments.

Thank you for your amazing error prone checker, it really helps to code better and avoid to make some common bug patterns.

[google-cla]

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[alexandrenavarro]

I just signed the CLA, I don't know how to rebuild the PR (just I tried close / reopen the PR).