We've been adding `disable!` calls with a future date to casks using
an unsigned app. That implicitly deprecates the cask until it reaches
the disable date, so we've been having to add simple `livecheck`
blocks to casks that use a default check to ensure that livecheck
continues to check them. It was suggested that it would be simpler to
have livecheck not skip casks that have a `disable!` call with a
`because: :unsigned` argument and I agree, so this modifies
`SkipConditions` to add a special case for this scenario.
ff2b1d6821