[A11y] Focus changes to custom editor when clicking on notebook toolbar overflow menu

Does this issue occur when all extensions are disabled?: No (requires custom editor)

• VS Code Version: 1.89.0-insider
• OS Version: Mac Sonoma 14.4.1

Steps to Reproduce:

1. Run the custom-editor-sample in the extension samples repository and open a .pawDraw or .cscratch file

2. Create a new notebook editor (ipynb file) in side by side orientation

3. First focus the notebook and observe that the tab title is highlighted

4. Now click the toolbar overflow button and observe that the custom editor tab is now highlighted

The focus should not change here but it does.