[WASM] Add OptIn to declaration with JsExport

libraries/kotlin.test/wasm/src/main/kotlin/kotlin/test/TestApi.kt

@@ -41,6 +41,7 @@ internal var currentAdapter: FrameworkAdapter = TeamcityAdapter()
 
 // This is called from the js-launcher alongside wasm start function
 @JsExport
+@OptIn(kotlin.js.ExperimentalJsExport::class)
 internal fun startUnitTests() {
     // This will be filled with the corresponding code during lowering
 }