Event description from the notifications mail is displayed as a string

Tested on an instance of XWiki 15.5.3 where XWIKI-21589 doesn't reproduce.

Steps to reproduce

1. Login as Admin
2. Setup the Mail Sending on the instance
3. Create an user (e.g. U1) with a valid email address
4. Login with the user and on his profile, on "Word-Based Notification" tab, insert a query (e.g. "Query2")
5. Click on the Notifications Bell and make sure all Watch Notification Toggles are ON
6. Login as Admin
7. Create a page (e.g. 'Pag1') and add the previously set query in its content (e.g. "Query2")
8. Login as Admin
9. Go to <server>/xwiki/bin/view/Scheduler/ and click on "Trigger" button for the 'Notifications daily email' job
10. Observe the notification events in the email received by the user

Expected results

The notification event related to Word-Based Notification app from the mail received by the user has a proper description, e.g.:

Pag1 has been updated by Administrator and contains 1 new occurrences of Query2 (on a total of 1)

Actual results

The notification event's description is:

notifications.events.org.xwiki.contrib.wordnotification.internal.notification.MentionedWordsRecordableEvent.description.by.1user