Update dependency express to v4.21.2

Author: renovate[bot]

package.json

@@ -15,7 +15,7 @@
   "homepage": "https://netboot.xyz",
   "dependencies": {
     "ejs": "3.1.10",
-    "express": "4.19.2",
+    "express": "4.21.2",
     "http": "0.0.0",
     "isbinaryfile": "5.0.2",
     "js-yaml": "4.1.0",