### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Im using localstack via a local minikube cluster using the helm charts:

https://github.com/localstack/helm-charts

Ive set up the following topic and endpoint:

```bash
  awslocal sns create-topic --name test
  awslocal sns subscribe \
    --protocol http \
    --topic-arn arn:aws:sns:us-east-1:000000000000:test \
    --endpoint-url http://localstack:4566 \
    --notification-endpoint http://myapp:8000/subscribe
```

Ive got some code in a where I publish a message in the topic manually via boto3, and it calls my endpoint successfully  which I can also confirm from my logs of the pod running the endpoint:

` INFO:     10.244.0.40:40552 - "POST /subscribe HTTP/1.1" 200 OK`

However immediately after, I get an error from localstack pod that looks like:


```

 2023-04-01T01:15:55.238  INFO --- [   sns_pub_0] l.services.sns.publisher   : Received error on sending SNS message, putting to DLQ (if configured): object supporting the buffer API required
 2023-04-01T01:15:55.239 ERROR --- [   sns_pub_0] l.services.sns.publisher   : An internal error occurred while trying to send the SNS message SnsMessage(type='Notification', message={'default': {'foo': 'bar'}}, message_attributes={}, message_structure='json', subject='example subject', message_deduplication_id=None, message_group_id=None, token=None, message_id='6f150269-fe84-4daf-876f-9c7cfae99f87')
 Traceback (most recent call last):
   File "/opt/code/localstack/localstack/services/sns/publisher.py", line 444, in _publish
     store_delivery_log(message_context, subscriber, success=True, delivery=delivery)
   File "/opt/code/localstack/localstack/services/sns/publisher.py", line 853, in store_delivery_log
     "messageMD5Sum": md5(message),
   File "/opt/code/localstack/localstack/utils/strings.py", line 145, in md5
     m.update(to_bytes(string))
 TypeError: object supporting the buffer API required
 
 During handling of the above exception, another exception occurred:
 
 Traceback (most recent call last):
   File "/opt/code/localstack/localstack/services/sns/publisher.py", line 80, in publish
     self._publish(context=context, subscriber=subscriber)
   File "/opt/code/localstack/localstack/services/sns/publisher.py", line 451, in _publish
     store_delivery_log(message_context, subscriber, success=False)
   File "/opt/code/localstack/localstack/services/sns/publisher.py", line 853, in store_delivery_log
     "messageMD5Sum": md5(message),
   File "/opt/code/localstack/localstack/utils/strings.py", line 145, in md5
     m.update(to_bytes(string))
 TypeError: object supporting the buffer API required
```

From what I can tell, this doesnt appear to be a result of any code or data im in control or at least I dont believe it is but i could be wrong. As I mentioned, my subscription endpoint appears to work as expected and the exception is raised internally after from the local stack modules. Any direction on how I might be able to address this bug and prevent the exception would be great, thanks.


Thanks.

### Expected Behavior

Interanal exception doesnt occur after publish to topic.

### How are you starting LocalStack?

Custom (please describe below)

### Steps To Reproduce

As described in behavior.


### Environment

```markdown
- OS: Pop!_OS 22.04
- LocalStack: 1.4 
```


### Anything else?

As requested.
import contextlib
import json
import logging
import queue
import random
import time
from io import BytesIO
from operator import itemgetter
import pytest
import requests
import xmltodict
from botocore.exceptions import ClientError
from pytest_httpserver import HTTPServer
from werkzeug import Response
from localstack import config
from localstack.aws.accounts import get_aws_account_id
from localstack.aws.api.lambda_ import Runtime
from localstack.services.sns.constants import PLATFORM_ENDPOINT_MSGS_ENDPOINT