Add end to end `xcversion install` test.

[Kesin11]

ref #361

Add end to end test with GitHub Actions. It checks xcversion install works properly with several Xcode versions.

If you want to check result of this test, you can see it in my forked repository.
Kesin11#4

@milch or someone who has admin access to this repository please do setup for enable this test.

1. Enable GitHub Actions. This feature is still beta.
2. Get an AppleID with 2FA disabled.
3. Set XCODE_INSTALL_USER and XCODE_INSTALL_PASSWORD to repository secrets.

[milch]

Thanks for the PR! 🥇 This will really help increase our confidence in the PRs we get here.
I have push access but I’m not actually an admin so I can’t enable GitHub Actions. @joshdholtz help?

IIRC for the downloads you just need any old Apple ID, so we could probably create one that’s throwaway with 2FA disabled

[joshdholtz]

@milch You are now an admin 😊 Feel free to DM me on Twitter if you need something faster in the future 😉

[milch]

Awesome, thanks! I'll merge this now and set up the Apple ID.

Thanks again @Kesin11!