Only query xcode version on macs when running itms transporter

[znerol]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

Attempting to run itms transporter results in the following message when run on Linux:

Unable to locate Xcode. Please make sure to have Xcode installed on your machine

Description

Only query xcode version when running on a mac.

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[KrauseFx]

Awesome, nice catch, thanks for your contribution @znerol 👍

[fastlane-bot]

Hey @znerol 👋

Thank you for your contribution to fastlane and congrats on getting this pull request merged 🎉
The code change now lives in the master branch, however it wasn't released to RubyGems yet.
We usually ship about once a week, and your PR will be included in the next one.

Please let us know if this change requires an immediate release by adding a comment here 👍
We'll notify you once we shipped a new release with your changes 🚀

[fastlane-bot]

Congratulations! 🎉 This was released as part of fastlane 2.62.0 🚀