Merge branch '18745-fix' into 'master'

Fix a 'wrong number of arguments' error

## What does this MR do?

Fixes #18745.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

To fix #18745.

## What are the relevant issue numbers?

Fixes #18745.

## Does this MR meet the acceptance criteria?

- [ ] Tests
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4757

app/services/notification_service.rb

@@ -222,7 +222,7 @@ class NotificationService
   end
 
   def accept_group_invite(group_member)
-    mailer.member_invite_accepted_email(group_member.id).deliver_later
+    mailer.member_invite_accepted_email(group_member.real_source_type, group_member.id).deliver_later
   end
 
   def decline_group_invite(group_member)