bug(overlay): Weird tooltip issue with the new popover overlay.

### Is this a regression?

- [x] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

v20

### Description

We detected a weird issue with tooltips regarding the popover introduced in v21.
When I put a tooltip on a mat-select, hover over the mat-select, the tooltip is shown. Then I open the mat select and move out my mouse from the browser and bring the mouse back to the browser, the tooltip is shown no matter where i am hovering on with my mouse.
Usually, it is solved after the mat select is closed and opened, then i cannot repro anymore.
But reloading the page and doing it the first time is usually a good repro for the issue.

I'm not sure if I could explain the repro correctly, so here is a short gif:

I scrolled through issues that can be related to my issue, and found this one: https://github.com/angular/components/issues/32642
Turning off the new popover with
`{ provide: OVERLAY_DEFAULT_CONFIG, useValue: { usePopover: false } },` solves the issue.
I cannot reproduce it anymore with usePopover: false.

### Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-3qpcms44?file=package.json,src%2Fmain.ts
Steps to reproduce:
1. Open the page the first time
2. Hover over the mat select
3. Open the mat select
4. Move the mouse outside of the browser
5. Bring back the mouse
6. The tooltip will be shown no matter where i hover over on the page

### Expected Behavior

The tooltip should not be shown everywhere.

### Actual Behavior

The tooltip is shown everywhere.

### Environment

- Angular: v21.1.2
- CDK/Material: v21.1.2
- Browser(s): Chrome latest
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

Inizia dalla riproduzione StackBlitz collegata, in particolare da package.json e src/main.ts, e segui i passaggi tooltip/mat-select con usePopover abilitato. Conferma il comportamento al primo caricamento in Chrome; il lavoro è completato quando il tooltip non viene più mostrato in tutta la pagina dopo aver lasciato e riaperto il browser, mentre il tooltip normale continua ad apparire sul mat-select.

Scritto dal modello di indicizzazione a partire dal testo della issue.