Reject redundant minimum macOS dependencies #24020

depends_on macos: :big_sur requires a release every supported macOS already meets. Homebrew/OSDependsOn now reports minimum macOS versions at or below the runtime floor and autocorrects the plain top-level form to depends_on :macos; OS-block, multi-key, tagged and commented forms get guidance instead. The floor comes from MacOSVersion::SYMBOLS and a spec pins it to HOMEBREW_MACOS_OLDEST_ALLOWED.

A bare depends_on :macos in on_arm/on_intel now means no minimum on that architecture and Cask/NoOverrides accepts it opposite a versioned block. Both cookbooks are updated.

Current taps have 14 casks and 5 formulae to clean up.

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Claude Code (Fable 5.1) drafted the implementation and tests; I reviewed the diff, verified the new tests fail without the change and pass with it, and ran brew lgtm --online plus targeted specs.