This flag allows you to specify formulae to upgrade, even if
`$HOMEBREW_BUNDLE_NO_UPGRADE` is set.
This is useful for upgrading specific formulae without upgrading all
formulae.
While we're here, let's add Sorbet signatures to the `Bundle` module
because I needed to add a new method there anyway.
We've had requests for this in Homebrew/bundle a few times so let's
implement it both for there and for `brew edit`.
Tested on my machine with `cursor` and working as expected.
