MySQL Flexible deployment fails when properties.maintenanceWindow is set

**Bicep version**
```PS /Users/matthewschmitt/GIT/bicep-registry-modules> bicep --version Bicep CLI version 0.28.1 (ba1e9f8c1e)
PS /Users/matthewschmitt/GIT/bicep-registry-modules> az bicep version
A new Bicep release is available: v0.29.45. Upgrade now by running "az bicep upgrade".
Bicep CLI version 0.27.1 (4b41cb6d4b)
```

**Describe the bug**
When passing a maintenanceWindow configuration to Microsoft.DBforMySQL/flexibleServers@2023-12-30, receive an error:

`Status Message: The server '*****' does not exist or in unexpected status. (Code:ServerNotExist)`

**To Reproduce**
Using the default tests case code below against the AVM module: https://github.com/Azure/bicep-registry-modules/tree/main/avm/res/db-for-my-sql/flexible-server
```module testDeployment '../../../main.bicep' = [
for iteration in ['init', 'idem']: {
scope: resourceGroup
name: '${uniqueString(deployment().name, enforcedLocation)}-test-${serviceShort}-${iteration}'
params: {
name: '${namePrefix}${serviceShort}001'
location: enforcedLocation
administratorLogin: 'adminUserName'
administratorLoginPassword: password
skuName: 'Standard_D2ds_v4'
tier: 'GeneralPurpose'
maintenanceWindow: {
customWindow: 'Enabled'
dayOfWeek: 0
startHour: 0
startMinute: 0
}
}
}
]
```
Expected behavior is that a Flexible server is created.

Start in the AVM module at avm/res/db-for-my-sql/flexible-server and inspect the default testDeployment in main.bicep. Reproduce the deployment with the supplied maintenanceWindow settings, then trace the Microsoft.DBforMySQL/flexibleServers@2023-12-30 definition. Done means the init and idem deployments create the Flexible server without the ServerNotExist error.

Written by the indexing model from the issue text.