docs: upgrade Node.js to version 20

Node.js 20 is the current LTS release:
https://nodejs.org/en/about/releases/

BREAKING CHANGE: the minimum Node.js is 20

.github/workflows/check-docs.yaml

@@ -95,7 +95,7 @@ jobs:
 
       - uses: actions/setup-node@v4
         with:
-          node-version: "18.x"
+          node-version: "20.x"
 
       - name: Keep npm cache around to speed up installs
         uses: actions/cache@v3

.github/workflows/test-and-release.yaml

@@ -90,7 +90,7 @@ jobs:
 
       - uses: actions/setup-node@v4
         with:
-          node-version: "18.x"
+          node-version: "20.x"
 
       - name: Keep npm cache around to speed up installs
         uses: actions/cache@v3
@@ -122,7 +122,7 @@ jobs:
       - uses: actions/download-artifact@v3
       - uses: actions/setup-node@v4
         with:
-          node-version: "18.x"
+          node-version: "20.x"
       - name: Keep npm cache around to speed up installs
         uses: actions/cache@v3
         with:

docs/project/SystemRequirements.rst

@@ -7,8 +7,8 @@ You need a Linux development environment with
 
 - `Git <https://git-scm.com/>`_
 - `jq <https://stedolan.github.io/jq/>`_
-- the `LTS release candidate of Node.js <https://nodejs.org/en/about/releases/>`_ (current LTS release is version 18)
-- the `current stable release of npm (version 8) <https://github.blog/changelog/2021-10-07-npm-cli-upgraded-to-version-8/>`_
+- the `LTS release candidate of Node.js <https://nodejs.org/en/download>`_ (current LTS release is version 20)
+- the `current stable release of npm (version 9) <https://github.blog/changelog/2022-11-09-npm-cli-v9-is-now-generally-available/>`_
 - `OpenSSL v3 <https://www.openssl.org/source/>`_ (for the certificate generation helpers)
 
 If you are using Windows, use the `Windows Subsystem for Linux <https://docs.microsoft.com/en-us/windows/wsl/install-win10>`_ with `Ubuntu 22.04

package.json

@@ -60,7 +60,7 @@
     ]
   },
   "engines": {
-    "node": ">=18",
+    "node": ">=20",
     "npm": ">=9"
   },
   "release": {