Matrix Hookshot doesn't send correctly formatted HTML for GitHub releases when Markdown isn't used

**Describe the bug**
I have bot that publishes releases for [one of my projects](/makedeb/makedeb), and part of that behavior involves automatically parsing my markdown file and getting the needed sections from it.

I'm using a Python library to do such (BeautifulSoup in particular), and I thus need to convert my markdown to html for it to be processed. Likewise, after I get my needed code, I publish my releases notes as raw HTML from the content in my markdown file, and there's thus (presumably) no markdown code itself in the releases.

Matrix Hookshot seems to be getting this raw HTML and escaping it or something, as upon viewing it in my room, I'm seeing raw HTML and not formatted HTML like I'd expect.

**To Reproduce**
1. Make a GitHub release with raw HTML
2. See raw HTML in Matrix client

**Expected behavior**
Formatted HTML

**Screenshots**

**Desktop (please complete the following information):**
- OS: Ubuntu 20.04
- Browser: Element Desktop
- Version: 1.10.10

**Additional context**
N/A

Begin by locating the GitHub release handling and the HTML conversion or escaping path; no file or test is identified in the report. Reproduce with a release whose notes contain raw HTML, then verify in Element that the release appears as formatted HTML rather than literal tags.

Written by the indexing model from the issue text.