PR authors get email notifications on task completion even when they unwatch that specific PR

Summary

When the author of a PR unwatches this specific Pull request, they continue to receive email notifications for any tasks created/completed/deleted in the comments of this PR.

Steps to Reproduce

1. Create a Pull Request in Bitbucket Cloud repo, with a Bitbucket account account1
2. Create a comment in this PR, and a few tasks in that comment
3. Unwatch the Pull Request
4. Log in to Bitbucket with a different account, account2
5. Open the previously created PR, and mark the tasks as completed

Expected Results

account1's email does not receive any notifications for task completion

Actual Results

account1's email keeps receiving notifications for task completion