Drop support for Node v18 (require v20.19+)

Node v18 has been EOL since March 2025.

The noble libraries require v20.19+,
so we align with those to avoid development warnings.

.github/workflows/tests.yml

@@ -31,7 +31,7 @@ jobs:
     strategy:
       fail-fast: false # if tests for one version fail, continue with the rest
       matrix:
-        node-version: [18.x, 20.x, 22.x, 24.x]
+        node-version: [20.x, 22.x, 24.x]
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
 
     name: Node ${{ matrix.node-version }}

package-lock.json

@@ -56,7 +56,7 @@
         "web-streams-polyfill": "^4.2.0"
       },
       "engines": {
-        "node": ">= 18.0.0"
+        "node": ">= 20.19.0"
       }
     },
     "node_modules/@babel/code-frame": {

package.json

@@ -5,7 +5,7 @@
   "license": "LGPL-3.0+",
   "homepage": "https://openpgpjs.org/",
   "engines": {
-    "node": ">= 18.0.0"
+    "node": ">= 20.19.0"
   },
   "keywords": [
     "crypto",