Closing HTML tags getting removed from Custom Header content inside of a script tag. #2914

Describe the bug
When putting custom HTML inside of a <script> tag, all closing tags are removed.

Steps To Reproduce
Steps to reproduce the behavior:

1. Start with a fresh install of BookStack
2. Add the following to the Custom HTML Head Content:

<script>
<div></div>
</script>

3. View the page source on any page in the wiki.
4. See that the inserted content is only:

<script>
<div>
</script>

Expected behavior
I expected the closing tags to not be scrubbed from the custom HTML field.

Your Configuration (please complete the following information):

• Exact BookStack Version (Found in settings): v21.08.2
• PHP Version: 7.4.21
• Hosting Method (Nginx/Apache/Docker): Nginx

Additional context
I am attempting to work on a new solution for custom Markdown parsing, resolving ticket #2761