Strip escape codes from annotations.

[reitermarkus]

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• Have you successfully run brew tests with your changes locally?

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Otherwise you end up with annotations like this:

download not possible: Checksum for Cask 'rescuetime' does not match.
Expected: �[32me4a150a0e9278a32c787475c7549b5af47634b0061146e69552bc02a6396a2bf�[0m
  Actual: �[31m41f0f340ec75b8296756e4129f6df8743279ddfd77f581d825839c7d7725088f�[0m
    File: /Users/runner/Library/Caches/Homebrew/downloads/6c16425385932119cb691c50100bf4fe56fbd2c9979a4db3433801a155ebf112--RescueTimeInstaller.pkg
To retry an incomplete download, remove the file above.
If the issue persists, visit:
  �[4mhttps://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/reporting_bugs/checksum_does_not_match_error.md�[24m