[BUG][AWS::SNS::Subscription] Failed to update CFN stack with error "Invalid parameter: FilterPolicyScope: Invalid value [null]"

### Name of the resource

AWS::SNS::Subscription

### Resource Name

_No response_

### Issue Description

When using Cloudformation resource [AWS::SNS::Subscription](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-sns-subscription.html#cfn-sns-subscription-filterpolicyscope) to create the SNS subscription. At first, it could successfully deploy the template with following format:
```
AWSTemplateFormatVersion: 2010-09-09
Resources:
SNSS2M2HB:
Type: 'AWS::SNS::Subscription'
Properties:
TopicArn: 'arn:aws:sns:ap-northeast-1:9068199XXXXX:FargateTaskNotification'
Endpoint: 'arn:aws:lambda:ap-northeast-1:9068199XXXXX:function:event-puller'
Protocol: lambda
FilterPolicy: '{"stage": ["dev"]}'
FilterPolicyScope: MessageAttributes
```

When tried to remove the "FilterPolicyScope" section, the CFN stack updated failed with error message:

```
Invalid parameter: FilterPolicyScope: Invalid value [null]. Please use either MessageBody or MessageAttributes (Service: AmazonSNS; Status Code: 400; Error Code: InvalidParameter; Request ID: cd9f6761-d459-50ba-8bf3-3ad740f2e744; Proxy: null)
```

I also tried to update stack with by removing filter policy and filter policy scope. However, we always got the error message "FilterPolicyScope: Invalid value [null]".

```
AWSTemplateFormatVersion: 2010-09-09
Resources:
SNSS2M2HB:
Type: 'AWS::SNS::Subscription'
Properties:
TopicArn: 'arn:aws:sns:ap-northeast-1:9068199XXXXX:FargateTaskNotification'
Endpoint: 'arn:aws:lambda:ap-northeast-1:9068199XXXXX:function:event-puller'
Protocol: lambda
```

### Expected Behavior

The SNS API seems not accepted null value on "FilterPolicyScope". The CloudFormation should not keep invoke the "SetSubscriptionAttributes" with "null" value when we remove the "FilterPolicyScope". Also, per document mentioned, that field is optional.

### Observed Behavior

With my investigation, I found the CFN invoked SNS API "SetSubscriptionAttributes" with following request parameter on every update behavior.

```
"eventTime": "2023-04-14T22:19:14Z",
"eventSource": "sns.amazonaws.com",
"eventName": "SetSubscriptionAttributes",
"awsRegion": "ap-northeast-1",
"sourceIPAddress": "cloudformation.amazonaws.com",
"userAgent": "cloudformation.amazonaws.com",
"errorCode": "InvalidParameterException",
"errorMessage": "Invalid parameter: FilterPolicyScope: Invalid value [null]. Please use either MessageBody or MessageAttributes",
"requestParameters": {
"subscriptionArn": "arn:aws:sns:ap-northeast-1:9068199XXXXX:sandbox-pubsub-record_store-20220928:c2beccc1-f1fe-4d3c-969e-701c660e6c74",
"attributeName": "FilterPolicyScope"
},
"responseElements": null,
```

### Test Cases

1) Create the Stack with following template:

```
AWSTemplateFormatVersion: 2010-09-09
Resources:
SNSS2M2HB:
Type: 'AWS::SNS::Subscription'
Properties:
TopicArn: 'arn:aws:sns:ap-northeast-1:9068199XXXXX:FargateTaskNotification'
Endpoint: 'arn:aws:lambda:ap-northeast-1:9068199XXXXX:function:event-puller'
Protocol: lambda
FilterPolicy: '{"stage": ["dev"]}'
FilterPolicyScope: MessageAttributes
```

2) Remove both "FilterPolicyScope" and "FilterPolicy"

### Other Details

_No response_

Start by reproducing the two CloudFormation stack updates from the issue templates and inspect the SNS SetSubscriptionAttributes request. The fix is complete when removing FilterPolicy and FilterPolicyScope no longer sends a null FilterPolicyScope value and the stack update succeeds.

Written by the indexing model from the issue text.