fix: do not try and remove Mono on ARM

[SMillerDev]

As warned in https://github.com/Homebrew/homebrew-cask/actions/runs/9734259421?pr=178098

Important: Do not tick a checkbox if you haven’t performed its action. Honesty is indispensable for a smooth review process.

In the following questions <cask> is the token of the cask you're submitting.

After making any changes to a cask, existing or new, verify:

• [ ] The submission is for a stable version or documented exception.
• [ ] brew audit --cask --online <cask> is error-free.
• [ ] brew style --fix <cask> reports no offenses.

Additionally, if adding a new cask:

• [ ] Named the cask according to the token reference.
• [ ] Checked the cask was not already refused (add your cask's name to the end of the search field).
• [ ] brew audit --cask --new <cask> worked successfully.
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