Changelog titles are inconsistent when having a short label

[stof]

Bug Report

Q	A
Version(s)	5.3.0

Summary

When a label name is only 2 characters long (for instance CI in that case), the generated changelog uses a different heading level for that label than for longer labels.

Current behavior

See https://github.com/doctrine/DoctrineBundle/releases/tag/2.13.2 for a case. the generated release note looks like that:

### Release Notes for [2.13.2](https://github.com/doctrine/DoctrineBundle/milestone/107)

2.13.x bugfix release (patch)

### 2.13.2

- Total issues resolved: **0**
- Total pull requests resolved: **4**
- Total contributors: **4**

CI
--

 - [1852: Drop Psalm in favor of PHPStan](https://github.com/doctrine/DoctrineBundle/pull/1852) thanks to @greg0ire

#### Bug

 - [1851: There is no ProxyManagerBridge v7](https://github.com/doctrine/DoctrineBundle/pull/1851) thanks to @derrabus
 - [1841: Fix compatibility for Symfony 6 projects without doctrine/persistence 3 support](https://github.com/doctrine/DoctrineBundle/pull/1841) thanks to @alexander-schranz

#### Documentation

 - [1840: Fix extraneous index:: in docs](https://github.com/doctrine/DoctrineBundle/pull/1840) thanks to @W0rma

How to reproduce

1. Create a label named CI in your repo (as well as a longer one for comparison
2. Create one PR for each label and merge them
3. Trigger a release containing those PRs

Expected behavior

The CI heading should be consistent with other labels, using a <h4> rather than a <h2>