Attempting to update notification email for sub-group shows 404 page
### Summary
Updating the notification email address used for a sub-group throws a 404. Doing the same thing for a root level group works as expected.
### Steps to reproduce
1. Visit https://gitlab.com/profile/notifications
1. Update the notification email for a root level group, it works
1. Attempt to update notification email for a sub-group, you will get a generic 404
### What is the current *bug* behaviour?
Throwing a 404 when attempting to update a sub-group notification email address
### What is the expected *correct* behaviour?
Not to see a 404 and have that groups notification email updated
### Relevant logs and/or screenshots
A (mostly) useless(?) video

issue