Build UIKitBackend in CI

[bbrk24]

Only includes the build step and not the test step because xcodebuild -scheme swift-cross-ui-Package test errors out looking for GTK headers.

[bbrk24]

Maybe I should've done a matrix rather than a bash for loop 😅

[bbrk24]

After piping the logs through xcpretty:

❌  /Users/runner/work/swift-cross-ui/swift-cross-ui/Sources/UIKitBackend/KeyboardToolbar.swift:197:30: 'UIToolbar' is unavailable in tvOS

final class KeyboardToolbar: UIToolbar {
                             ^~~~~~~~~

It seems to have found a legitimate error. I'll fix that I guess.

[bbrk24]

As stupid as this looks:

@available(iOS 14, macCatalyst 14, tvOS 14, *)
@available(tvOS, unavailable)

It failed to compile if I removed tvOS 14 from the former annotation.

Edit: posted to the forums https://forums.swift.org/t/contradictory-available-s-are-required/78831

[stackotter]

Thanks for this! 🙏 Very useful