ci: install serverless version after npm update not global

Author: Jeff Gordon

.github/workflows/validate.yml

@@ -69,7 +69,7 @@ jobs:
           npm update --no-save
           npm update --save-dev --no-save
       - name: Install serverless
-        run: npm install -g serverless@${{ matrix.sls-version }}
+        run: npm install serverless@${{ matrix.sls-version }}
 
       - name: Validate Prettier formatting
         run: npm run prettier-check:updated