GH Actions: Bump DavidAnson/markdownlint-cli2-action from 17 to 18

Bumps [DavidAnson/markdownlint-cli2-action](https://github.com/davidanson/markdownlint-cli2-action) from 17 to 18.
- [Release notes](https://github.com/davidanson/markdownlint-cli2-action/releases)
- [Commits](DavidAnson/markdownlint-cli2-action@v17...v18)

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

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

.github/workflows/reusable-markdownlint.yml

@@ -26,4 +26,4 @@ jobs:
       # @link https://github.com/marketplace/actions/markdownlint-cli2-action
       - name: Check markdown with CLI2
         if: ${{ steps.has_config.outputs.files_exists == 'true' }}
-        uses: DavidAnson/markdownlint-cli2-action@v17
+        uses: DavidAnson/markdownlint-cli2-action@v18