Commit history atom feed - self reference doesn't match document location
## What
When running the commit history atom feed through W3 atom feed validator, there is a complaint about the `rel="self"` associated. This should be addressed
> *Self reference doesn't match document location*
>
> This feed is valid, but interoperability with the widest range of feed readers could be improved by implementing the following recommendations.
>
> line 4, column 155: Self reference doesn't match document location [help]
>
> ... rel="self" type="application/atom+xml"/>
> ^
## Links
- Validator: https://validator.w3.org/feed/
- Relevant help link: https://validator.w3.org/feed/docs/warning/SelfDoesntMatchLocation.html
## Original thread
The following discussion from !65599 should be addressed:
- [ ] @afontaine started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/65599#note_626103008): (+2 comments)
> I've noticed the W3 atom feed validator has some complaints regarding the rel="self" link doesn't match. Should we update that as well, in a follow-up?
issue