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Cask::Audit#audit_min_os uses the minimum macOS version requirement from the app bundle and newest item in the Sparkle feed but these values are treated equally in the code. We recently came across a cask where the app specified High Sierra (10.13) as the minimum macOS version but the Sparkle appcast used 26.0.0 (Tahoe) as the minimumSystemVersion value, so this audit incorrectly requires depends_on macos: ">= :tahoe" in the cask. The app and the upstream website both advertise the 10.13 macOS requirement, so the appcast value needs to be fixed.

However, this highlighted a shortcoming in the audit logic, as we probably shouldn't allow the Sparkle minimum macOS value to override what's specified in the app. This updates the logic to only fall back to the sparkle_min_os value when bundle_min_os is nil, so a higher Sparkle value won't override bundle_min_os.