[BUG] The tags property of User Assigned Identity resource shouldn't change the value

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/msi/resource-manager/Microsoft.ManagedIdentity/ManagedIdentity/stable/2023-01-31/ManagedIdentity.json

### API Spec version

2023-01-31

### Describe the bug

When we add tag "CreatedOnDate" with value "2022-07-08T23:50:21Z", service API always returns "2022-07-08 23:50:21". This is a regression issue since previously it wouldn't changed the value.

{
"location": "eastus",
"properties": {},
"tags": {
"CreatedOnDate": "2022-07-08T23:50:21Z"
}
}

The API response on Azure Portal:

### Expected behavior

Service API should return "2022-07-08T23:50:21Z" when we add tag "CreatedOnDate" with value "2022-07-08T23:50:21Z".

### Actual behavior

Service API returns "2022-07-08 23:50:21" when we add tag "CreatedOnDate" with value "2022-07-08T23:50:21Z".

### Reproduction Steps

Create User Assigned Identity with below tag.

{
"location": "eastus",
"properties": {},
"tags": {
"CreatedOnDate": "2022-07-08T23:50:21Z"
}
}

### Environment

PROD

Start with specification/msi/resource-manager/Microsoft.ManagedIdentity/ManagedIdentity/stable/2023-01-31/ManagedIdentity.json and reproduce the User Assigned Identity request using the tag value shown in the issue. Compare the service response with the API specification and confirm that the exact ISO-8601 string is preserved; the issue is done when the regression has an identified repository or service-level resolution.

Written by the indexing model from the issue text.