Image symbol used in `length_big` is only supported on macOS 15

[sentry-io]

Sentry Issue: CALENDR-1J

EXC_BREAKPOINT: Exception 6, Code 1, Subcode 4373345384
  File "<compiler-generated>", in value
  File "NSImage.swift", line 17, in NSImage.init
    self.init(systemSymbolName: systemName.description)!
  File "Icons.swift", line 36, in length_big
    static let length_big = NSImage(systemName: "textformat.characters.arrow.left.and.right")
  ?, in closure in AppearanceViewController.nextEventContent.getter
  ?, in AppearanceViewController.transparencyContent.getter
...
(40 additional frame(s) were not displayed)