ci(workflow): add 'npm' cache for actions/setup-node in .github/workflows

.github/workflows/test.yml

@@ -3,8 +3,7 @@ on:
   push:
     branches:
       - main
-  pull_request:
+  pull_request: null
-
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -16,6 +15,7 @@ jobs:
         uses: actions/setup-node@v2
         with:
           node-version: 12.x
+          cache: npm
 
       - name: Install dependencies
         run: npm install