build(deps): bump @metalsmith/markdown from 1.5.0 to 1.6.0 (#4625)

Bumps [@metalsmith/markdown](https://github.com/metalsmith/markdown) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/metalsmith/markdown/releases)
- [Changelog](https://github.com/metalsmith/markdown/blob/master/CHANGELOG.md)
- [Commits](metalsmith/markdown@v1.5.0...v1.6.0)

---
updated-dependencies:
- dependency-name: "@metalsmith/markdown"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -30,7 +30,7 @@
     "node": ">=12"
   },
   "dependencies": {
-    "@metalsmith/markdown": "^1.5.0",
+    "@metalsmith/markdown": "^1.6.0",
     "@metalsmith/permalinks": "^2.4.0",
     "autoprefixer": "^10.4.7",
     "graceful-fs": "^4.2.10",