build(deps): bump sanitize-html from 1.21.1 to 1.22.0 in /backend

Sourced from sanitize-html's changelog.

1.22.0: bumped htmlparser2 dependency to the 4.x series. This fixes longstanding bugs and should cause no bc breaks for this module, since the only bc breaks upstream are in regard to features we don't expose in this module.

• 5265a81 1.22.0: htmlparser2 4.x fixes longstanding bugs
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