[BUG] Major MySQL versions not supported

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/mysql/resource-manager/Microsoft.DBforMySQL/FlexibleServers/stable/2023-12-30/FlexibleServers.json#L774

### API Spec version

2023-12-30

### Describe the bug

The current major MySQL version 8.4 is not supported by the API. This is critical, as after manual update, API access as well as terraform access to the ressource is impossible.

See: https://learn.microsoft.com/en-us/azure/mysql/concepts-version-policy#supported-mysql-versions

Related; https://github.com/Azure/azure-rest-api-specs/issues/32480

### Expected behavior

Supported Versions should be:

5.7, 8.0.21, 8.4.x, 9.3.x

### Actual behavior

8.4.x, 9.3.x are not supported.

### Reproduction Steps

Create a MySQL flexible database server using the API with version 8.4.x fails.

### Environment

- Terraform

Start with specification/mysql/resource-manager/Microsoft.DBforMySQL/FlexibleServers/stable/2023-12-30/FlexibleServers.json at the referenced line and inspect the allowed MySQL versions. Update the supported versions to match the issue, then verify that creating a MySQL flexible server with version 8.4.x succeeds through the API.

Written by the indexing model from the issue text.