chore: use node version from nvmrc in github action

.github/workflows/node.js.yml

@@ -1,7 +1,4 @@
-# This workflow will do a clean installation of node dependencies, cache/restore them, build the source code and run tests across different versions of node
-# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-nodejs
-
-name: Node.js CI
+name: Dassie CI
 
 on:
   push:
@@ -15,19 +12,18 @@ jobs:
   build:
     runs-on: ubuntu-latest
 
-    strategy:
-      matrix:
-        node-version: [ 20.x ]
-        # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
-
     steps:
       - name: Checkout
         uses: actions/checkout@v3
 
+      - name: Read .nvmrc
+        run: echo "NVMRC=$(cat .nvmrc)" >> $GITHUB_OUTPUT
+        id: nvmrc
+
       - name: Install Node.js
         uses: actions/setup-node@v3
         with:
-          node-version: ${{ matrix.node-version }}
+          node-version: "${{ steps.nvmrc.outputs.NVMRC }}"
 
       - uses: pnpm/action-setup@v2
         name: Install pnpm