Revert back to supporting Swift 5.5

[liamnichols]

👋

While working on CreateAPI/CreateAPI#83, I noticed that Xcode 13.2 tests failed because Get 1.0.0 bumped the Swift requirement up to 5.6. While I am not opposed to dropping support for older versions of Xcode, I don't want to do it if there isn't a good reason to.

I was going to tag you on the CreateAPI Pull Request, but I first wanted to check if the project still compiled using Xcode 13.2 since I didn't see any surrounding commits/discussion, and at this point, I thought it was just easier to raise a PR here instead 😄

Anyway, my question is: Does Get need to drop support for Swift 5.5 just yet? Even if we got at least one tagged release under 1.0.0, this would allow CreateAPI to require both Get 1.0.0 while still supporting Swift 5.5.

If you are happy to keep it, I've included in this PR some updates to the CI checks to make sure that we test Swift 5.5 on both macOS and Linux. But equally, if there is a reason not to revert the change then I think I can just do the same over in CreateAPI as well.

If you do merge this PR, would it be possible to tag a release over the next few days to unblock me?

Thanks again!

[kean]

I'm OK to keep 5.5 support. The general idea is to support the latest version from the previous stable release + the latest, which is going to be Xcode 14. Well, technically it isn't out. I've been using it for a few weeks though.

[liamnichols]

Thanks for that @kean. I agree that when Xcode 14 goes public (hopefully next month) its worth going back to 5.6 minimum. This is a massive help for now though!

I did just notice that I forgot to update the table in README.md. Want me to submit a PR to update it or are you happy not sharing that you support 5.5 publicly given that we'll like drop it again in the coming months?

[kean]

It's all good, I'll update it.