Added support for Node 20

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

- this adds support for Node 20 as it is LTS and meets our support
  criteria

.github/workflows/unit-test.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [ 18.x ]
+        node: [ 18.x, 20.x ]
     env:
       FORCE_COLOR: 1
     name: Node ${{ matrix.node }}

package.json

@@ -39,7 +39,7 @@
     ]
   },
   "engines": {
-    "node": "^12.22.1 || ^14.17.0 || ^16.13.0 || ^18.0.0"
+    "node": "^12.22.1 || ^14.17.0 || ^16.13.0 || ^18.0.0 || ^20.11.1"
   },
   "preferGlobal": true,
   "dependencies": {