fix: ignore quarantine for linux cask download

[WangEdward]

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Override the quarantine method for cask download on Linux. This should, in most cases, allow bump-cask-pr to function on Linux.

[Bo98]

Shouldn't Quarantine.available? return false on Linux? It checks for a working xattr.

The original quarantine method you're overriding has a return unless Quarantine.available?

[SMillerDev]

Seems fine for me.

Actually Bo's comment makes more sense

[Bo98]

I think I see the issue:

brew/Library/Homebrew/cask/quarantine.rb

Line 36 in 141ac15

if !system_command(xattr, args: ["-h"], print_stderr: false).success?

This should probably be if xattr.nil? || !system_command(xattr, ...

[MikeMcQuaid]

Makes sense and thanks for suggestion @Bo98.

Thanks so much for your contribution! Without people like you submitting PRs we couldn't run this project. You rock, @WangEdward!