Bump markdown-link-check from 3.12.2 to 3.13.6

Bumps [markdown-link-check](https://github.com/tcort/markdown-link-check) from 3.12.2 to 3.13.6.
- [Release notes](https://github.com/tcort/markdown-link-check/releases)
- [Changelog](https://github.com/tcort/markdown-link-check/blob/master/CHANGELOG.md)
- [Commits](tcort/markdown-link-check@v3.12.2...v3.13.6)

---
updated-dependencies:
- dependency-name: markdown-link-check
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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