Getting `InvalidPolicyParameters` error when configuring logAnalyticsWorkspace retention days

[web-app-loganalytics](https://github.com/Azure/azure-quickstart-templates/tree/master/quickstarts/microsoft.web/web-app-loganalytics)

### Issue Details
My bicep:
```
resource logAnalyticsWorkspace 'Microsoft.OperationalInsights/workspaces@2020-08-01' = {
name: logAnalyticsName
location: resourceGroup().location
properties: {
sku: {
name: 'PerGB2018'
}
retentionInDays: 365
features: {
enableLogAccessUsingOnlyResourcePermissions: true
}
}
}
```

This error disappeared after I remove `retentionInDays` property. How can I set this property with Bicep?

Detailed error messages:
```
{
"code": "InvalidPolicyParameters",
"message": "A function or parameter in policy assignment 'acat-custom-policy-set-assignment' associated with the policy definition 'log-analytics-workspace-retention' could not be validated. Please either fix the policy or remove the policy assignment to unblock. If using template functions, try following the tips in: https://aka.ms/policy-avoiding-template-failures. The inner error is 'The template language function 'length' expects its parameter to be an array, object, or a string. The provided value is of type 'Integer'. Please see https://aka.ms/arm-template-expressions/#length for usage details.'."
}
```

Start with the web-app-loganalytics quickstart and its Microsoft.OperationalInsights/workspaces resource, then trace the acat-custom-policy-set-assignment and log-analytics-workspace-retention names from the error. Confirm why retentionInDays: 365 reaches the policy's length call; done means the quickstart deploys with retentionInDays set and the policy validation error is gone.

Written by the indexing model from the issue text.