- Found with
`grep -rL "# typed: strict" Library/Homebrew | xargs grep -l "undef "`.
- This stops people from trying to bump them and
getting an error that they can't fix because
[it's a Sorbet limitation](https://sorbet.org/docs/error-reference#3008),
wasting contributor time.
This wasn't working with casks because the bottle tag
would be nil here.
It was refactored to not use the bottle tag because
casks don't have bottles.
I also moved the valid_casks? method to extend/os/mac
because casks only run on macOS and the generic OS
tests were failing before.
