[BUG] ResourceHealth, "refreshTimestamp" property value is not RFC3339

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/resourcehealth/resource-manager/Microsoft.ResourceHealth/preview/2023-10-01-preview/ResourceHealth.json

### API Spec version

2023-10-01-preview

### Describe the bug

Azure requires date-time property conform to RFC3339 (in model).

Issue reported by customer, see https://github.com/Azure/azure-sdk-for-java/issues/43927

### Expected behavior

date-time value from server by RFC3339, e.g. `"2025-01-24T09:06:10Z"`.

### Actual behavior

Server response is `"2025-01-24 09:06:10Z"`.

### Reproduction Steps

call EmergingIssues_List, check value in "refreshTimestamp" property
https://github.com/Azure/azure-rest-api-specs/blob/main/specification/resourcehealth/resource-manager/Microsoft.ResourceHealth/preview/2023-10-01-preview/ResourceHealth.json#L1036

### Environment

_No response_

Start with the ResourceHealth.json definition near line 1036 and the EmergingIssues_List response described in the issue. Compare the declared date-time format with the reported server value, then identify whether the repository can address the mismatch; done means the RFC3339 requirement and the affected response are correctly resolved or clearly handed to the service owner.

Written by the indexing model from the issue text.