Wrong link sent in Role Requests notifications to Slack

In notifications_slack plugin, the links for Role Requests are under `/requests/` instead of `/role-requests/` ([ref](https://github.com/discord/access/blob/b693c2acea12b33b5cab33854921b6d4cf9b97e1/examples/plugins/notifications/notifications.py#L174)).

<img width="1155" height="700" alt="screenshot" src="https://github.com/user-attachments/assets/3fb740c7-ea5f-4c73-9e15-7601f34fd2e9" />