[Bug]: Tabs overflow button remains visible when there is no more scroll in RTL

### Code of conduct

- [x] I agree to follow this project's code of conduct.

### Impacted component(s)

sp-tabs-overflow

### Expected behavior

When the tabs overflow has reached the end of the scroll container, the tabs overflow button should not be visible.

### Actual behavior

The tabs overflow button appears even when there is no more overflow.

### Screenshots

### What browsers are you seeing the problem in?

_No response_

### How can we reproduce this issue?

1. Go to https://opensource.adobe.com/spectrum-web-components/storybook/index.html?path=/story/tabs-overflow-sizes--m&globals=system:express;textDirection:rtl
2. Click on the tabs overflow button until Tab Item 20 is visible
3. Observe the tabs overflow button still visible

### Sample code or abstract reproduction which illustrates the problem

_No response_

### Severity

SEV 3

### Logs taken while reproducing problem

_No response_

Start with the sp-tabs-overflow component and reproduce the issue in the linked Storybook story with textDirection:rtl. Click the overflow button until Tab Item 20 is visible, then inspect how the component determines whether more scrolling is available. Done means the overflow button is hidden when the tabs have reached the end of the scroll container.

Written by the indexing model from the issue text.