Ensure app can be built on xcode 14, since xcode 15 is in beta

[DAcodedBEAT]

upstream PR: creepymonster#564

Previous PR description:

Currently the following error is reported when building with the latest stable Xcode: Error: Value of type 'EKEventStore' has no member 'requestFullAccessToEvents'.

requestFullAccessToEvents is a new method only available in iOS 17, which is in beta, and is also only supported by Xcode 15, which is also in beta.

Since this feature is dependent on beta APIs which aren't available on older Xcodes, this application will not build. As a result, this conditional needs additional safeguards in order to compile properly on the latest stable Xcode.

note: Since there isn't a way to check which version of Xcode is used, I needed to check based on the available Swift version, which is published on Apple's documentation: https://developer.apple.com/support/xcode/

Resolves creepymonster#563