[K/N] Adjust moved special backend checks tests

^KT-61564

compiler/testData/diagnostics/nativeTests/specialBackendChecks/objCInterop/t30.kt

@@ -1,8 +1,11 @@
+// FIR_IDENTICAL
+// WITH_PLATFORM_LIBS
 import kotlinx.cinterop.*
 import platform.darwin.*
 import platform.Foundation.*
 
 class Zzz : NSAssertionHandler() {
+    @OptIn(kotlinx.cinterop.BetaInteropApi::class)
     @ObjCOutlet
     var NSObject.x: NSObject
         get() = this