Fix duplicate undoable mutation commits on notification exit

[dawNotPoi]

Problem

With MUI 6 and later, Notification passes the same onExited callback through both the legacy TransitionProps API and slotProps.transition. MUI invokes both callbacks, causing an undoable mutation to be committed twice.

Fixes #11334

Solution

Use TransitionProps and ContentProps only with MUI 5. For MUI 6 and later, use the slot props API exclusively while preserving the existing user prop override order.

How To Test

• yarn jest packages/ra-ui-materialui/src/layout/Notification.spec.tsx --runInBand
• yarn jest packages/ra-core/src/notification/useNotify.spec.tsx --runInBand
• yarn workspace ra-core build
• yarn workspace ra-ui-materialui build
• yarn tsc --noEmit -p packages/ra-ui-materialui/tsconfig.json

Additional Checks

• The PR targets master for a bug fix
• The PR includes unit tests
• No new story is required because this is internal transition wiring covered by the regression test
• No documentation change is required because the public API is unchanged