fix: only emit `for_await_track_reactivity_loss` in async mode (#16644)

Helps with #16610  (but does not fix it yet)

.changeset/tender-masks-bow.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: only emit `for_await_track_reactivity_loss` in async mode

packages/svelte/src/compiler/phases/3-transform/client/visitors/ForOfStatement.js

@@ -8,7 +8,12 @@ import { dev, is_ignored } from '../../../../state.js';
  * @param {ComponentContext} context
  */
 export function ForOfStatement(node, context) {
-	if (node.await && dev && !is_ignored(node, 'await_reactivity_loss')) {
+	if (
+		node.await &&
+		dev &&
+		!is_ignored(node, 'await_reactivity_loss') &&
+		context.state.options.experimental.async
+	) {
 		const left = /** @type {VariableDeclaration | Pattern} */ (context.visit(node.left));
 		const argument = /** @type {Expression} */ (context.visit(node.right));
 		const body = /** @type {Statement} */ (context.visit(node.body));