chore(deps): update dependency markdownlint-cli2 to v0.21.0

| datasource | package           | from   | to     |
| ---------- | ----------------- | ------ | ------ |
| npm        | markdownlint-cli2 | 0.20.0 | 0.21.0 |

Author: renovate[bot]

package-lock.json

@@ -12,7 +12,7 @@
     "lint:check:md": "markdownlint-cli2"
   },
   "devDependencies": {
-    "markdownlint-cli2": "0.20.0",
+    "markdownlint-cli2": "0.21.0",
     "prettier": "3.8.1"
   }
 }