fix: address untracked_writes memory leak (#15694)

* fix-untracked-writes-leak

* fix

* fix

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

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

.changeset/pretty-dingos-unite.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: address untracked_writes memory leak

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

@@ -476,7 +476,7 @@ export function update_reaction(reaction) {
 		// we need to increment the read version to ensure that
 		// any dependencies in this reaction aren't marked with
 		// the same version
-		if (previous_reaction !== null) {
+		if (previous_reaction !== reaction) {
 			read_version++;
 
 			if (untracked_writes !== null) {