fix: Bump mockito to breaking change with fixes

[srawlins]

Description

mockito 5.0.0-nullsafety.6 includes a breaking change to the signature of Mock.noSuchMethod. This PR bump mockito and changes firebase_auth and firebase_core tests to match the new signature.

Related Issues

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[srawlins]

Not sure what to do about the current CI errors. Does it have to do with Flutter test version pinning?

[russellwheatley]

Hey @srawlins, thanks for the PR! Mockito upgrades were merged in this here:#5014 so I'm going to close this one 👍