[Fix #792] Fixes a false negative for Rails/RedundantPresenceValidationOnBelongsTo

[PedroAugustoRamalhoDuarte]

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Fix a false negative for Rails/RedundantPresenceValidationOnBelongsTo when belongs_to have one block and one hash like belongs_to :company, -> { where(foo: true) }, inverse_of: :employee

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• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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[koic]

Thanks for opening this PR. Can you squash your commits into one?

[koic]

Can you squash your commits into one?

@PedroAugustoRamalhoDuarte ping :-)

[PedroAugustoRamalhoDuarte]

@koic Done!!

[koic]

Thanks!