use macos-latest for ui-showcase build on CI

[whyoleg]

In #3662 test started to fail on ui-showcase module because of ERROR CLASS.
This was fixed in #3663 and everything was fine locally.
But on CI we were building ui-showcase on Linux - and so before #3662 there were no macOS specific declarations there.
So we need to build it on macOS.
Looks like we need to do the same on TC. @adam-enko could you help here? Is it possible to run only UiShowcaseIntegrationTest on TC on macOS? Other tests should work fine with linux runner.

[adam-enko]

Is it possible to run only UiShowcaseIntegrationTest on TC on macOS?

I think the best approach would be to skip tests on a case-by-case basis using JUnit.

import org.junit.jupiter.api.Assumptions.assumeTrue

@Test
fun foo() {
  assumeTrue(System.getProperty("os.name").lowercase().contains("mac"), "test requires macOS")
  // ...
}

EDIT: Actually, there's a built in annotation for this.

https://junit.org/junit5/docs/5.2.0/api/org/junit/jupiter/api/condition/EnabledOnOs.html

import org.junit.jupiter.api.condition.EnabledOnOs
import org.junit.jupiter.api.condition.OS

@Test
@EnabledOnOs(OS.MAC, disabledReason = "...")
fun foo() {
  // ...
}

@EnabledOnOs can also be added to UiShowcaseIntegrationTest so it will enable/disable all tests in the class.

[vmishenev]

I do not know how ui-showcase is used in UI testing. Is it ok for @berezinant to build the project only on macOS?

[berezinant]

To build the project only on macOS will not be a problem for development
The only thing that could be affected is that we plan to run screenshot tests for ui-showcase project on CI and maybe there would be difficulties

UPD I see that there is still a possibility to run screenshot's at least against macOS so this is not an issue either