adding bahmutov/npm-install to workflow

Author: gagoar

.github/workflows/validation.yml

@@ -28,6 +28,7 @@ jobs:
         with:
           node-version: 12.x
       - name: Install dependencies
+        uses: bahmutov/[email protected]
         run: npm install
       - name: Mocha
         run: npm run test:only