Steps to reproduce:

1. PHP 8.3.10, Phorge at 58f1c83a5ac56073a1960772c78c99ece72d4729
2. Create a task with a task description which @mentions two usernames
3. These users automatically become task subscribers.
4. Remove the two users from the Subscribers field.
5. Edit the task description, e.g. by adding a character.

Expected outcome:
As the users were unsubscribed, they should not get resubscribed, as no new interaction with these users happened and as the users were not (newly) mentioned (again).
(However, mentioned users should get subscribed at initial task creation when mentioned in the description.)

Actual outcome:
Users get forcefully re-subscribed to the task.

Other comments:

• This is obviously different from quoting the previous comment of another user in a comment. Quoting Evan from https://secure.phabricator.com/T11035: "In particular, this means that @mentioning a user in a new comment will re-add them. I think this is expected/desirable: you're explicitly calling them back to the task."
• Downstream https://phabricator.wikimedia.org/T96464 mentions clicking Mute Notifications as a workaround but this is not intuitive (and not immediately obvious why the user should use that hammer if the user already unsubscribed anyway).