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

We have not the best CI runner in the world (Azure Pipelines), and we trying to move to self-hosted runners with M1 CPUs. Unfortunately, Azure Pipelines agent runs everything under Rozetta (microsoft/azure-pipelines-agent#3184), and we want to put arch -arm64 before xcodebuild while archiving our targets.

Additionally, we used the xcodebuild_command option in scan, and were surprised that gym still misses it despite the fact scan uses GYM_XCODE_BUILD_COMMAND ENV var for this option. If you need me to change the ENV var name in scan ping me, and I'll do it.

Description

Copy-pasted everything related to xcodebuild_command from scan 😅 and covered it with a test.

Also, I removed env NSUnbufferedIO=YES prefix for the default xcodebuild_command value in the gym action, cause so far it worked well without it.

Testing Steps

scan(xcodebuild_command: `echo 'Hello, World!'; xcodebuild`)