fix(deps): update dependency ngx-markdown to v21

Author: renovate[bot]

demo/package.json

@@ -16,7 +16,7 @@
     "@angular/router": "21.0.0-rc.2",
     "angular-ecmascript-intl": "../dist/angular-ecmascript-intl",
     "marked": "^17.0.0",
-    "ngx-markdown": "^20.0.0",
+    "ngx-markdown": "^21.0.0",
     "prismjs": "^1.30.0",
     "tslib": "^2.8.1"
   },