restore removal of !is_flushing_sync check in Batch.ensure

Needed on async-another-try-pt-3 (async-fork-branch-merge).

packages/svelte/src/internal/client/reactivity/batch.js

@@ -933,7 +933,7 @@ export class Batch {
 		if (current_batch === null) {
 			const batch = (current_batch = new Batch());
 
-			if (!is_processing && !is_flushing_sync) {
+			if (!is_processing) {
 				queue_micro_task(() => {
 					if (!batch.started) {
 						batch.flush();