Github actions: use node version from nvmrc

actions/setup-node#32 (comment)

.github/workflows/astro.yml

@@ -7,7 +7,7 @@ name: Deploy Astro site to Pages
 on:
   # Runs on pushes targeting the default branch
   push:
-    branches: ["main"]
+    branches: ['main']
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
@@ -20,11 +20,11 @@ permissions:
 
 # Allow one concurrent deployment
 concurrency:
-  group: "pages"
+  group: 'pages'
   cancel-in-progress: true
 
 env:
-  BUILD_PATH: "." # default value when not using subfolders
+  BUILD_PATH: '.' # default value when not using subfolders
   # BUILD_PATH: subfolder
 
 jobs:
@@ -54,7 +54,7 @@ jobs:
       - name: Setup Node
         uses: actions/setup-node@v3
         with:
-          node-version: "16"
+          node-version-file: '.nvmrc'
           cache: ${{ steps.detect-package-manager.outputs.manager }}
           cache-dependency-path: ${{ env.BUILD_PATH }}/package-lock.json
       - name: Setup Pages