build: bump html-pipeline from 2.12.2 to 2.12.3 in /docs

Bumps [html-pipeline](https://github.com/jch/html-pipeline) from 2.12.2 to 2.12.3.
- [Release notes](https://github.com/jch/html-pipeline/releases)
- [Changelog](https://github.com/jch/html-pipeline/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jch/html-pipeline/compare/v2.12.2...v2.12.3

)

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