Bump DavidAnson/markdownlint-cli2-action from 19 to 20

Bumps [DavidAnson/markdownlint-cli2-action](https://github.com/davidanson/markdownlint-cli2-action) from 19 to 20.
- [Release notes](https://github.com/davidanson/markdownlint-cli2-action/releases)
- [Commits](https://github.com/davidanson/markdownlint-cli2-action/compare/v19...v20)

---
updated-dependencies:
- dependency-name: DavidAnson/markdownlint-cli2-action
  dependency-version: '20'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/github.yml

@@ -408,7 +408,7 @@ jobs:
             python3 CI/validate_json.py
 
         - name: Validate Markdown
-          uses: DavidAnson/markdownlint-cli2-action@v19
+          uses: DavidAnson/markdownlint-cli2-action@v20
           with:
             config: 'CI/example.markdownlint-cli2.jsonc'
             globs: '**/*.md'