Bump ezyang/htmlpurifier from 4.11.0 to 4.12.0

Bumps [ezyang/htmlpurifier](https://github.com/ezyang/htmlpurifier) from 4.11.0 to 4.12.0.
- [Release notes](https://github.com/ezyang/htmlpurifier/releases)
- [Changelog](https://github.com/ezyang/htmlpurifier/blob/master/NEWS)
- [Commits](https://github.com/ezyang/htmlpurifier/compare/v4.11.0...v4.12.0

)

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