[Bug] lightning-modal disableClose ineffective when LWS is enabled

 API: lightning/modal (LightningModal)
- Property: disableClose
- Expected: close button should be suppressed
- Actual: Modal still closes despite disableClose = true
- Condition: LWS enabled (Locker not in effect)
- Reproducible: 100% / Intermittent
- API Version: xx.x
- Org Type: Sandbox / Production / Scratch Org
- Workaround attempted: [none / custom CSS / manual event interception]