Resolve "Autolinking includes trailing exclamation marks"

What does this MR do?

Makes our new Rinku-less autolinking match the previous behaviour in https://github.com/vmg/rinku/blob/v2.0.1/ext/rinku/autolink.c#L65

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

Don't think so!

Why was this MR needed?

The refactor in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17180 introduced a regression.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend

What are the relevant issue numbers?

Closes #44587 (closed).