[ux] Scrolling down, no loading indicator is shown

**Description**
When scrolling down a long list of label tasks there is no loading indicator shown when the end of the currently loaded batch has been reached and loading the next batch has begun (when there is more data to be loaded).

**To Reproduce**
Steps to reproduce the behavior:
1. Import a large dataset to label, I am guessing over several thousands of tasks
2. Click on 'Projects'
3. Click on your project with the recently imported tasks
4. Click an item
5. Scroll the tasks list (left side of the screen) down to the end.
6. Wait a few moments
7. Scroll the tasks list (left side of the screen) down again.
8. Observe new items are added to the scroll list, however no visual indication whas shown of the loading activity.

**Expected**
When the end of the currently loaded batch of tasks is reached, I expected to be shown a loading indication, so I know new data is being loaded.

**Environment (please complete the following information):**
- OS: macOS 26.2
- Label Studio Version [e.g. 1.22.0]