[Bug]: Cancel events close all modal overlays instead of only the top overlay

### Code of conduct

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

### Impacted component(s)

sp-overlay

### Library version

1.11.2

### Expected behavior

The cancel event should close only the modal overlay from where the event originated.

### Actual behavior

The cancel event closes all open modal overlays.

Example bug from Express: CCEX-276235

### Screenshots

_No response_

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

Chrome

### How can we reproduce this issue?

1. Have two modal overlays open
2. Dispatch a cancel event from one of the overlays
3. Observe both overlays closing

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

_No response_

### Severity

SEV 2

### Logs taken while reproducing problem

_No response_

### Would you like to track this issue in Jira?

- [x] Yes, please tell me the ticket number!

Start with the sp-overlay component and reproduce the issue using two open modal overlays, then dispatch a cancel event from one overlay. Done means the originating modal closes while the other remains open, matching the expected behavior described in the issue.

Written by the indexing model from the issue text.