fix serverless/MQEvent SourceAccessConfigurations property type

[InQuirer]

AWS docs/ref:

• https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-property-function-mq.html#sam-function-mq-sourceaccessconfigurations

fixes error:

• TypeError: <class 'troposphere.serverless.MQEvent'>: MQEvent.SourceAccessConfigurations is <class 'troposphere.awslambda.SourceAccessConfiguration'>, expected [<class 'str'>]

  Function(
  title='MyLambdaFunction',
  Events={
      "MQEvent": MQEvent(
          title="MQEvent",
          Broker='arn:aws:mq:us-east-2:123456789012:broker:MyBroker:b-1234a5b6-78cd-901e-2fgh-3i45j6k178l9',
          Queues=['my-queue'],
          SourceAccessConfigurations=[  # now it's array of [SourceAccessConfiguration]
              SourceAccessConfiguration(
                  Type="BASIC_AUTH",
                  URI='arn:aws:secretsmanager:us-east-1:01234567890:secret:MyBrokerSecretName',
              ),
              SourceAccessConfiguration(
                  Type="VIRTUAL_HOST",
                  URI="/",
              ),
          ],
      ),
  }
  )

[markpeek]

Thanks!