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

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

docs/Gemfile.lock

@@ -80,7 +80,7 @@ GEM
       octokit (~> 4.0)
       public_suffix (~> 3.0)
       typhoeus (~> 1.3)
-    html-pipeline (2.12.2)
+    html-pipeline (2.12.3)
       activesupport (>= 2)
       nokogiri (>= 1.4)
     html-proofer (3.15.0)