fix: forbid <style> tags in DOMPurify config

[abeatrix]

Currently the <style> tag is breaking Cody as reported in https://sourcegraph.slack.com/archives/C03CSAER9LK/p1698893918877999:

This PR adds 'style' to the FORBID_TAGS array in the DOMPurify config to prevent style tags from being allowed.

Test plan

1. Ask Cody :

Where is the styling defined for the code below?

<?xml version="1.0" encoding="utf-8"?>
<!-- Generator: Adobe Illustrator 27.5.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
	 viewBox="0 0 16 16" style="enable-background:new 0 0 16 16;" xml:space="preserve">
<style type="text/css">
	.st0{fill:none;stroke:#231F20;stroke-width:1.5;stroke-linecap:round;stroke-miterlimit:10;}
</style>
<path class="st0" d="M4,5.6h2.5"/>
<path class="st0" d="M11,3.8v2.5"/>
<path class="st0" d="M3.2,9.7c0,0,1.1,2.5,4.8,2.5s4.8-2.5,4.8-2.5"/>
</svg>

Before

After: