[K/N] Adjust moved special backend checks tests

^KT-61564

compiler/testData/diagnostics/nativeTests/specialBackendChecks/cInterop/t9.kt

@@ -1,7 +1,9 @@
+// FIR_IDENTICAL
 import kotlinx.cinterop.*
 
 fun foo(f: Function0<out Int>) = f
 
+@OptIn(kotlinx.cinterop.ExperimentalForeignApi::class)
 fun bar() {
     staticCFunction(::foo)
 }