style: fix deprecation date check

[Rylan12]

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Follow up to #8512
Blocking Homebrew/homebrew-core#60336 (and, consequently, the release of 2.5.0)

#8512 exposed a bug in rubocop that checked the first argument to disable! or deprecate! and assumed it was date:. When adding because: arguments to disable!, rubocop failed when trying to parse a reason as a date.

Running brew style on the following fails before this but succeeds after this PR:

deprecate! because: "is broken"

[MikeMcQuaid]

Thanks again @Rylan12!