livecheck/strategy: fix **unused type

[cho-m]

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Based on https://sorbet.org/docs/sigs#rest-parameters, the method signature seems to be for the values of remaining keyword arguments.

In the sorbet doc example, the **kwargs has method signature type kwargs: Float and becomes T::Hash[Symbol, Float] in the method body.

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Noticed when running brew livecheck -r --debug <formula> which would output

Parameter 'homebrew_curl': Expected type T.nilable(T::Hash[Symbol, T.untyped]), got type FalseClass

[reitermarkus]

Thanks!

[MikeMcQuaid]

Thanks @cho-m!