run lint only once

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ on:
     branches: [master]
 
 jobs:
-  build:
+  install:
     runs-on: ubuntu-latest
 
     strategy:
@@ -25,5 +25,26 @@ jobs:
         with:
           node-version: ${{ matrix.node-version }}
           cache: 'npm'
+        env:
+          CACHE_KEY: npm-cache-key-node-v${{ matrix.node-version }}
       - run: npm i
+  lint:
+    needs: install
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [12]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v2
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: 'npm'
+        env:
+          CACHE_KEY: npm-cache-key-node-v${{ matrix.node-version }}
+      - run: npm i # by now, dependencies have been cached
       - run: npm run lint