ci: remove deprecated lambda executor from localstack config (#6771)

* remove deprecated lambda executor from localstack config

* mount docker socket in localstack container

Author: rochdev

.github/workflows/serverless.yml

@@ -78,10 +78,11 @@ jobs:
           EXTRA_CORS_EXPOSE_HEADERS: x-amz-request-id,x-amzn-requestid,x-amz-id-2
           AWS_DEFAULT_REGION: us-east-1
           FORCE_NONINTERACTIVE: 'true'
-          LAMBDA_EXECUTOR: local
           START_WEB: '0'
         ports:
           - 4566:4566
+        volumes:
+          - /var/run/docker.sock:/var/run/docker.sock:rw
       # we have two localstacks since upgrading localstack was causing lambda & S3 tests to fail
       # To-Do: Debug localstack / lambda and localstack / S3
       localstack-legacy: