Fix "Discover JCB" -> "Discover" | "JCB", refine StripeStatic.cardType
Fix "Discover JCB" -> "Discover" | "JCB", refine StripeStatic.cardType

Fixed bug previously introduced due to misread documentation.
Refined the return type of `StripeStatic.cardType`, `string` => `StripeCardDataBrand`.
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