Dropped support for Node 14 and 16

ref https://linear.app/tryghost/issue/ENG-765/add-support-for-node-20

- these versions are EOL and we should no longer support them

package.json

@@ -38,7 +38,7 @@
     "web": "https://ghost.org"
   },
   "engines": {
-    "node": "^14.18.0 || ^16.13.0 || ^18.12.1 || ^20.11.1"
+    "node": "^18.12.1 || ^20.11.1"
   },
   "license": "MIT",
   "bugs": {