Increase minimum supported macOS building version from Sonoma 14 to Sequoia 15

[rgoldberg]

Increase minimum supported macOS building version from 14 Sonoma to 15 Sequoia:

• /usr/bin/jq
• /usr/bin/trash
• Remove argument for withTaskGroup(of: Void.self)
• Swift 6.2.1
  • Deploys to macOS 11+
  • .swiftSetting(.strictMemorySafety(true))
  • NonisolatedNonsendingByDefault
  • Swift Testing 6.2.1
    • exit tests
      • stdout & stderr capturing?
  • https://github.com/apple/swift-configuration
• Swift 6.1
  • Deploys to macOS 10.13+
• .swiftlint.yml: remove some unused_import: allowed_transitive_imports: