https://github.com/Homebrew/brew/pull/15754 fixed
`Cask::URL::DSL#initialize`, but we also need to fix
`Cask::URL#initialize` as that takes the same parameters.
Error:
```
Error: Cask 'mycask' definition is invalid: 'url' stanza failed
with: Parameter 'using': Expected type T.nilable(Symbol), got type Class
with value MyCustomDownloadStrategy
Caller:
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/sorbet-runtime-0.5.10461/lib/types/private/methods/call_validation.rb:113
```
Refs: https://github.com/Homebrew/brew/issues/15750