Allow --display-times with --cask

[toobuntu]

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Options --cask and --display-times do not need to be mutually exclusive with brew install, brew reinstall and brew upgrade.

eb16e10 added recording of cask installation times but didn't update the conflicts.

install.rb had a faulty return if condition that prevented execution of periodic clean or displaying installation times in cask-only installs. This was because installed_formulae.empty? would always evaluate to true.

Ref: https://github.com/orgs/Homebrew/discussions/5262

brew typecheck on arm64 led me to this bug sorbet/sorbet#6778

[MikeMcQuaid]

Good catch, thanks again for another great PR @toobuntu!