Bump markdownlint-rule-helpers from 0.20.0 to 0.21.0

Bumps [markdownlint-rule-helpers](https://github.com/DavidAnson/markdownlint) from 0.20.0 to 0.21.0.
- [Changelog](https://github.com/DavidAnson/markdownlint/blob/main/CHANGELOG.md)
- [Commits](v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: markdownlint-rule-helpers
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

package.json

@@ -86,7 +86,7 @@
     "markdown-it-for-inline": "0.1.1",
     "markdown-it-sub": "1.0.0",
     "markdown-it-sup": "1.0.0",
-    "markdownlint-rule-helpers": "0.20.0",
+    "markdownlint-rule-helpers": "0.21.0",
     "npm-run-all": "4.1.5",
     "strip-json-comments": "5.0.1",
     "terser-webpack-plugin": "5.3.9",