chore(deps): update node.js to v24.21.0

Author: renovate-bot

package.json

@@ -21,6 +21,6 @@
     "sinon": "~21.1"
   },
   "volta": {
-    "node": "24.18.0"
+    "node": "24.21.0"
   }
 }

packages/asciidoctor/package.json

@@ -73,6 +73,6 @@
     "pug": "^3.0.3"
   },
   "volta": {
-    "node": "24.18.0"
+    "node": "24.21.0"
   }
 }

packages/core/package.json

@@ -67,7 +67,7 @@
   },
   "homepage": "https://github.com/asciidoctor/asciidoctor.js",
   "volta": {
-    "node": "24.18.0"
+    "node": "24.21.0"
   },
   "peerDependencies": {
     "highlight.js": "^11.0.0"