APIM Backend Pool can not deploy

**Bicep version**
0.27.1

**Describe the bug**
deploy backendpool (Microsoft.ApiManagement/service/backends)
Raise ValidationError
```
ERROR: error executing step command 'provision': deployment failed: failing invoking action 'provision', error deploying infrastructure: deploying to subscription:

Deployment Error Details:
ValidationError: One or more fields contain incorrect values:
ValidationError: Url is not supported for backend pool.
ValidationError: Protocol is not supported for backend pool.
ValidationError: One or more fields contain incorrect values:
ValidationError: Url is not supported for backend pool.
ValidationError: Protocol is not supported for backend pool.
```

**To Reproduce**
deploy this bicep template.

```
resource apimBackend_0 'Microsoft.ApiManagement/service/backends@2023-05-01-preview' = {
parent: apimService
name: 'my-chat-backend0'
properties: {
description: 'backend0'
type: 'Single'
protocol: 'http'
url: openaiApiUrl
}
}

resource apimBackend_pool 'Microsoft.ApiManagement/service/backends@2023-05-01-preview' = {
parent: apimService
name: 'my-chat-backendpool'
properties: {
description: 'chat-backendpool'
protocol: 'http'
type: 'Pool'
url: 'http://localhost'
pool: {
services: [
{
id: apimBackend_0.id
}
]
}
}
}

```

**Additional context**
I deployed same template 2024/05/13, it's OK.
But today, I try to chnage backend URLs, it raise above Error.

I update azd and bicep to latest versions.
But Error is not resolve.

VSCode syntax checker require protocol and type filelds.
Deployment raise Error, fields is not supported.
I can't understand.....

Start from the reproduced Bicep template for Microsoft.ApiManagement/service/backends@2023-05-01-preview and compare the pool declaration with the deployment validation errors. Run the template deployment while checking the backend pool's supported fields; done means the pool deploys without the Url or Protocol validation errors.

Written by the indexing model from the issue text.