Move cask fixtures to `test/fixtures/cask`.

Library/Homebrew/cask/spec/support/Casks/with-binary.rb

.../Homebrew/cask/spec/support/Casks/with-embedded-binary.rb

Library/Homebrew/cask/spec/support/file_helper.rb

Library/Homebrew/cask/test/cask/artifact/alt_target_test.rb

Library/Homebrew/cask/test/cask/artifact/app_test.rb

Library/Homebrew/cask/test/cask/artifact/uninstall_test.rb

Library/Homebrew/cask/test/cask/artifact/zap_test.rb

.../Homebrew/cask/test/support/Casks/appdir-interpolation.rb

Library/Homebrew/cask/test/support/Casks/auto-updates.rb

Library/Homebrew/cask/test/support/Casks/bad-checksum.rb

Library/Homebrew/cask/test/support/Casks/container-7z.rb

Library/Homebrew/cask/test/support/Casks/container-air.rb

Library/Homebrew/cask/test/support/Casks/container-bzip2.rb

Library/Homebrew/cask/test/support/Casks/container-cab.rb

Library/Homebrew/cask/test/support/Casks/container-dmg.rb

Library/Homebrew/cask/test/support/Casks/container-gzip.rb

Library/Homebrew/cask/test/support/Casks/container-lzma.rb

Library/Homebrew/cask/test/support/Casks/container-pkg.rb

Library/Homebrew/cask/test/support/Casks/container-rar.rb

Library/Homebrew/cask/test/support/Casks/container-sit.rb