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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description
When I call the Lambda PutFunctionEventInvokeConfig API using the aws-java-sdk, the sdk throws an exception claiming it cannot parse the LastModified timestamp in the response:
```
software.amazon.awssdk.core.exception.SdkClientException: Unable to parse date : 2021-05-28T16:02:30.018Z
        at software.amazon.awssdk.core.exception.SdkClientException$BuilderImpl.build(SdkClientException.java:98)
        at software.amazon.awssdk.protocols.core.StringToInstant.lambda$safeParseDate$0(StringToInstant.java:77)
        at software.amazon.awssdk.protocols.core.StringToInstant.convert(StringToInstant.java:54)
        at software.amazon.awssdk.protocols.core.StringToInstant.convert(StringToInstant.java:32)
```

For comparison, the response for a getting a FunctionEventInvokeConfig for a Lambda of a real AWS account using the aws-cli is the following:
```
{
    "LastModified": "2021-05-27T19:26:43.454000-07:00",
    "FunctionArn": "...",
    ...
}
```

## Expected behavior
LambdaAsyncClient in aws-java-sdk should correctly parse the response for a PutFunctionEventInvokeConfig request.

## Actual behavior
LambdaAsyncClient in aws-java-sdk throws an exception when parsing the LastModified field in the response.

# Steps to reproduce

## Command used to start LocalStack
```
docker run -d --rm --name localstack -p 4566:4566 localstack/localstack:latest
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
```
val putEventInvokeConfigRequest =
  PutFunctionEventInvokeConfigRequest.builder
    .functionName(functionName)
    .maximumEventAgeInSeconds(21600)
    .maximumRetryAttempts(0)
    .build
lambdaClient.putFunctionEventInvokeConfig(putEventInvokeConfigRequest)
```


""" List event source mappings
        ---
        operationId: 'listEventSourceMappings'
    """
    region = LambdaRegion.get()
    event_source_arn = request.args.get('EventSourceArn')
    function_name = request.args.get('FunctionName')
    mappings = region.event_source_mappings
    if event_source_arn:
        mappings = [m for m in mappings if event_source_arn == m.get('EventSourceArn')]
    if function_name:
        function_arn = func_arn(function_name)
        mappings = [m for m in mappings if function_arn == m.get('FunctionArn')]
    response = {
        'EventSourceMappings': mappings
    }
    return jsonify(response)
@app.route('%s/event-source-mappings/<mapping_uuid>' % PATH_ROOT, methods=['GET'])
def get_event_source_mapping(mapping_uuid):