Internal server error when using pickZones function in a management group deployment but scoped to subscription

**Bicep version**
Bicep CLI version 0.4.1008 (223b8d227a)

**Describe the bug**
When deploying a VM I use the pickZones logic to see if it's going to use and availability set or zones, this works just fine in isolation running 'simplePickZones.bicep'.
When I connect this up to a larger deployment at the management group

**To Reproduce**
This code works fine when deployed
New-AzDeployment -Name 'test-deployment' -Location 'UKSouth' -TemplateFile .\Bicep\simple.pickZones.bicep

simple.pickZones.bicep
```bicep
targetScope = 'subscription'
//see if availabilityzones are available
var location = 'ukwest'
var zonesAvailable = !empty(pickZones('Microsoft.Compute', 'virtualMachines', location))
output zonesAvailable bool = zonesAvailable
```
If I call that module from a main file it will return InternalServerError
New-AzManagementGroupDeployment -Name 'test-deploy-mgmtGroup' -ManagementGroupId '_idOfManagementGroup_' -Location 'UKSouth' -TemplateFile .\Bicep\main.bicep

main.bicep
```bicep
// Deployment scope
targetScope = 'managementGroup'

module picktest './simple.pickZones.bicep' = {
name: 'DP-testModule'
scope: subscription('_subscriptionId_')
params: {
}
}

output zonesAvailable bool = picktest.outputs.zonesAvailable
```

Reproduce the deployment using simple.pickZones.bicep alone, then through main.bicep at management-group scope with the subscription module scope. Start at the pickZones call and the management-group-to-subscription deployment path. Done means the nested deployment no longer returns InternalServerError and produces the zonesAvailable output.

Written by the indexing model from the issue text.