chore: avoid microtasks when flushing sync (alternative)

.changeset/polite-melons-tickle.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: avoid microtasks when flushing sync

packages/svelte/src/internal/client/runtime.js

@@ -823,6 +823,8 @@ export function flushSync(fn) {
 	if (fn) {
 		is_flushing = true;
 		flush_queued_root_effects();
+
+		is_flushing = true;
 		result = fn();
 	}
 
@@ -831,6 +833,8 @@ export function flushSync(fn) {
 	while (queued_root_effects.length > 0) {
 		is_flushing = true;
 		flush_queued_root_effects();
+
+		is_flushing = true;
 		flush_tasks();
 	}