Use engines.node as source of version data for "actions/setup-node" action

.github/CONTRIBUTING.md

@@ -9,7 +9,9 @@
 Follow the installation instructions here:<br />
 https://nodejs.dev/download
 
-Node.js 20.x is used for development of this project. [nvm](https://github.com/nvm-sh/nvm) is recommended to easily switch between Node.js versions.
+The **Node.js** version in use is defined in the `engines.node` field of [`package.json`](../package.json).
+
+[nvm](https://github.com/nvm-sh/nvm) is recommended to easily switch between Node.js versions.
 
 ### 2. Install dependencies
 

.github/workflows/check-npm.yml

@@ -1,9 +1,5 @@
 name: Check npm
 
-env:
-  # See: https://github.com/actions/setup-node/#readme
-  NODE_VERSION: 20.x
-
 # See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
 on:
   push:
@@ -162,7 +158,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: ${{ env.NODE_VERSION }}
+          node-version-file: package.json
 
       - name: Install dependencies
         run: npm install

.github/workflows/check-packaging-ncc-typescript-npm.yml

@@ -1,9 +1,5 @@
 name: Check Packaging
 
-env:
-  # See: https://github.com/actions/setup-node/#readme
-  NODE_VERSION: 20.x
-
 on:
   push:
     paths:
@@ -35,7 +31,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: ${{ env.NODE_VERSION }}
+          node-version-file: package.json
 
       - name: Install dependencies
         run: npm install

.github/workflows/test.yml

@@ -1,9 +1,5 @@
 name: Test Action
 
-env:
-  # See: https://github.com/actions/setup-node/#readme
-  NODE_VERSION: 20.x
-
 on:
   push:
   pull_request:
@@ -31,7 +27,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: ${{ env.NODE_VERSION }}
+          node-version-file: package.json
 
       - name: npm install
         run: npm install

package.json

@@ -39,5 +39,8 @@
     "prettier": "^3.3.3",
     "ts-jest": "^28.0.8",
     "typescript": "^5.6.2"
+  },
+  "engines": {
+    "node": "20.x"
   }
 }