Merge branch '20233-confidential-issue' into 'master'

Show release notes in tag list

## What does this MR do?

Two things in one! Ensure that a tag's message having an invalid UTF-8 byte sequence doesn't cause a 500, like at: https://gitlab.com/bitcubate/node/tags?page=9 (The problem tag is https://gitlab.com/bitcubate/node/tags/v0.1.0)

Also ensure that the release notes are actually shown on the tag index, like they are supposed to.

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

There's not much, so all of it.

## Why was this MR needed?

The tags index was broken in two ways.

## What are the relevant issue numbers?

Closes #20233 but does more than that.

## Screenshots (if relevant)

Before:

![image](/uploads/5456fcc70f02794570762e6ed9c6d863/image.png)

After:

![image](/uploads/0329bf93e0f1be2417e500e924bc775d/image.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [ ] 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 !5503

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