feat: update UI export from MATIC to POL (#4720)

## Explanation

Updates a Notification Controller UI export from MATIC to POL

## References

https://consensyssoftware.atlassian.net/browse/NOTIFY-1138

## Changelog

### `@metamask/notification-services-controller`

- **CHANGED**: Update UI export from `MATIC` to `POL`

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've highlighted breaking changes using the "BREAKING" category
above as appropriate
- [x] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

packages/notification-services-controller/src/NotificationServicesController/ui/constants.ts

@@ -17,7 +17,7 @@ export const NOTIFICATION_NETWORK_CURRENCY_SYMBOL = {
   [NOTIFICATION_CHAINS_ID.BSC]: 'BNB',
   [NOTIFICATION_CHAINS_ID.LINEA]: 'ETH',
   [NOTIFICATION_CHAINS_ID.OPTIMISM]: 'ETH',
-  [NOTIFICATION_CHAINS_ID.POLYGON]: 'MATIC',
+  [NOTIFICATION_CHAINS_ID.POLYGON]: 'POL',
 };
 
 export type BlockExplorerConfig = {