[K/N] Adjust moved special backend checks tests

^KT-61564

compiler/testData/diagnostics/nativeTests/specialBackendChecks/concurrent/t49.kt

@@ -1,5 +1,7 @@
+// FIR_IDENTICAL
 import kotlin.native.concurrent.*
 
+@OptIn(ObsoleteWorkersApi::class)
 fun foo(x: Int) {
     val worker = Worker.start()
     worker.execute(TransferMode.SAFE, { "zzz" }) { s -> s + x.toString() }