cask/cask: ensure plist is readable before reading.

If we don't have permissions to read it, this will raise an exception
even although this whole call chain is very tolerant of nil values.

Library/Homebrew/cask/cask.rb

@@ -515,7 +515,7 @@ module Cask
     sig { returns(T.nilable(Homebrew::BundleVersion)) }
     def bundle_version
       @bundle_version ||= if (bundle = artifacts.find { |a| a.is_a?(Artifact::App) }&.target) &&
-                             (plist = Pathname("#{bundle}/Contents/Info.plist")) && plist.exist?
+                             (plist = Pathname("#{bundle}/Contents/Info.plist")) && plist.exist? && plist.readable?
         Homebrew::BundleVersion.from_info_plist(plist)
       end
     end