Fix/suppress some warnings

(cherry picked from commit d8a43c216925b3a9e1475b786978436835a57927)

kotlin-native/Interop/JsRuntime/src/main/kotlin/jsinterop.kt

@@ -139,5 +139,7 @@ fun JsValue.setter(property: String, string: String) {
 
 object ArenaManager {
     val globalArena = allocateArena()
+
+    @Suppress("VARIABLE_IN_SINGLETON_WITHOUT_THREAD_LOCAL")
     var currentArena = globalArena
-}
+}