test(studio): rename unpin test to match what it actually verifies

Review of the pin-aware group list refactor flagged the test name
claiming the group "closes" on unpin — it doesn't assert that, and
structurally the group re-opens (togglePin never touches openGroupId).
Retitled to describe only the return-to-stack behavior actually tested.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/studio/src/components/editor/PropertyPanel.test.tsx

@@ -783,7 +783,7 @@ describe("PropertyPanel — pinning", () => {
   );
 
   it(
-    "unpinning returns the group to its normal stack position and it closes",
+    "unpinning returns the group to its normal accordion stack position",
     async () => {
       const { host, root } = await renderPanel(true);
       const pinButton = host.querySelector<HTMLButtonElement>('[data-flat-group-pin="true"]');