Disable intermittent test (#2116)

# Pull Request

## 🤨 Rationale

Test failed again on unrelated PR:
https://github.com/ni/nimble/actions/runs/9104203860/job/25027598121?pr=2113

See #1891

## 👩‍💻 Implementation

Disabled as per policy.

## 🧪 Testing

N/A

## ✅ Checklist


- [x] I have updated the project documentation to reflect my changes or
determined no changes are needed.

change/@ni-nimble-components-93d068a3-17ea-4ecb-af3d-f9e01499a415.json

@@ -0,0 +1,7 @@
+{
+  "type": "none",
+  "comment": "Disable intermittent test",
+  "packageName": "@ni/nimble-components",
+  "email": "7282195+m-akinc@users.noreply.github.com",
+  "dependentChangeType": "none"
+}

packages/nimble-components/src/rich-text/mention-listbox/tests/mention-listbox.spec.ts

@@ -45,7 +45,8 @@ describe('RichTextMentionListbox', () => {
         await waitAnimationFrame(); // necessary because scrolling is queued with requestAnimationFrame
     }
 
-    it('should scroll the selected option into view when opened', async () => {
+    // Intermittent: see https://github.com/ni/nimble/issues/1891
+    xit('should scroll the selected option into view when opened', async () => {
         const model = new Model();
         const { connect, disconnect } = await setup500Options(model);
         await connect();