build(deps-dev): bump posthtml-markdownit from 3.1.1 to 3.1.2

Bumps [posthtml-markdownit](https://github.com/posthtml/posthtml-markdownit) from 3.1.1 to 3.1.2.
- [Release notes](https://github.com/posthtml/posthtml-markdownit/releases)
- [Commits](posthtml/posthtml-markdownit@v3.1.1...v3.1.2)

---
updated-dependencies:
- dependency-name: posthtml-markdownit
  dependency-version: 3.1.2
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]