Notifications sent twice on action

1. make a inclusion request
2. go to request detail page
3. try to accept the request
4. add comment in "Additional comments" box
5. Click accept

Bug:
the mail is sent twice, once for accept, the second time for the additional comment.

See:

Start by tracing the request-detail accept flow described in the reproduction, including submission of the “Additional comments” box and the notification dispatches for acceptance and comments. Identify why one action produces two emails, then verify that accepting with a comment sends only the intended notification and add or update a regression test if the repository provides a relevant test location.

Written by the indexing model from the issue text.