fix: use local value variable instead of next[key] in null check

Applies reviewer suggestion for consistency since value is already
assigned from next[key] on the line above.

Also adds required changeset for patch version bump.

.changeset/cuddly-cougars-grow.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: strip trailing semicolons in style directive reactive updates

packages/svelte/src/internal/client/dom/elements/style.js

@@ -12,7 +12,7 @@ function update_styles(dom, prev = {}, next, priority) {
 		var value = next[key];
 
 		if (prev[key] !== value) {
-			if (next[key] == null) {
+			if (value == null) {
 				dom.style.removeProperty(key);
 			} else {
 				// setProperty rejects values with trailing semicolons; strip them so that