The existing `LivecheckUrlProvided` RuboCop requires a `url` for all
`livecheck` blocks except those using `skip`, `formula`, or `cask`,
as those only appear in a `livecheck` block with no other DSL methods.
We now have a `throttle` method that can be used alongside other DSL
methods (e.g., `url`, `regex`, `strategy`) or by itself. `brew style`
currently fails when `throttle` is used by itself, so this reworks
the conditions to allow this usage.
b3ab410215