[K/N] Adjust moved special backend checks tests

^KT-61564

compiler/testData/diagnostics/nativeTests/specialBackendChecks/cInterop/t37.kt

@@ -1,6 +1,9 @@
+// FIR_IDENTICAL
+// OPT_IN: kotlin.native.internal.InternalForKotlinNative
 import kotlinx.cinterop.*
 import kotlinx.cinterop.internal.*
 
+@OptIn(kotlinx.cinterop.ExperimentalForeignApi::class)
 @CStruct(spelling = "struct { }") class Z constructor(rawPtr: NativePtr) : CStructVar(rawPtr) {
     val x: Pair<Int, Int>? = null
         @CStruct.MemberAt(offset = 0L) get