ci: Ensure to use latest major during tests

Author: pgrzesik

.github/workflows/test.yml

@@ -34,7 +34,7 @@ jobs:
         run: python -m pip install pipenv poetry
 
       - name: Install serverless
-        run: npm install -g serverless
+        run: npm install -g serverless@2
 
       - name: Install deps
         run: npm install