Use consistent node version

.github/workflows/build.yml

@@ -38,6 +38,7 @@ jobs:
     - name: Set up Node.js
       uses: actions/setup-node@v4
       with:
+        node-version-file: '.nvmrc'
         cache: 'npm'
     - run: npm ci
     - name: Cache PlatformIO
@@ -74,7 +75,7 @@ jobs:
       - name: Use Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '20.x'
+          node-version-file: '.nvmrc'
           cache: 'npm'
       - run: npm ci
       - run: npm test

.nvmrc

@@ -0,0 +1 @@
+20.18.1