chore: update test code

Author: horike37

__tests__/integration/eventbridge/multiple-integrations/service/serverless.yml

@@ -64,4 +64,4 @@ resources:
     YourBus:
       Type: AWS::Events::EventBus
       Properties:
-        Name: YourEventBus-${self:provider.stage}-multi
+        Name: YourEventBus-${sls:stage}-multi

__tests__/integration/eventbridge/single-integration/service/serverless.yml

@@ -23,4 +23,4 @@ resources:
     YourBus:
       Type: AWS::Events::EventBus
       Properties:
-        Name: YourEventBus-${self:provider.stage}-single
+        Name: YourEventBus-${sls:stage}-single