### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When calling 

`cloudWatchClient.EnableAlarmActions(&cloudwatch.EnableAlarmActionsInput{AlarmNames: alarmNames})`

with golang I receive a SerializationError with bytes in the error message saying: 

`<!DOCTYPE HTM |UBLIC "-//W3C//DTD HTML 3.2 Final//EN">.<title>500 Internal Server Error</title>.<h1>Internal Server Error</h1>.<p>The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.`

I believe this is a bug, since other cloudwatch operations like "DescribeAlarms" work flawlessly with the same client.

### Expected Behavior

I expected the call to go through without any errors

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

Start localstack, create alarms and call cloudwatch "EnableAlarmActions"

### Environment

_No response_

### Anything else?

_No response_
def test_put_metric_data(self, cloudwatch_client):
        metric_name = "metric-%s" % short_uid()
        namespace = "namespace-%s" % short_uid()
        
        data = [
            {
                "MetricName": metric_name,
                "Dimensions": [{"Name": "foo", "Value": "bar"}],
                "Timestamp": datetime(2019, 1, 3, tzinfo=tzutc()),
                "Unit": "Seconds",
            }
        ]
        rs = cloudwatch_client.put_metric_data(Namespace=namespace, MetricData=data)
        assert 200 == rs["ResponseMetadata"]["HTTPStatusCode"]
        
        rs = cloudwatch_client.get_metric_statistics(
            Namespace=namespace,
            MetricName=metric_name,
            StartTime=datetime(2019, 1, 1),
            EndTime=datetime(2019, 1, 10),
            Period=120,
            Statistics=["Average"],
        )
        assert metric_name == rs["Label"]
        assert 1 == len(rs["Datapoints"])
        assert data[0]["Timestamp"] == rs["Datapoints"][0]["Timestamp"]
        rs = cloudwatch_client.list_metrics(Namespace=namespace, MetricName=metric_name)
        assert 1 == len(rs["Metrics"])
        assert namespace == rs["Metrics"][0]["Namespace"]
    def test_put_metric_data_gzip(self, cloudwatch_client):