targetScope doesn't appear to support arrays

[furrm]

Bicep version
Bicep CLI version 0.3.255 (589f037)

Describe the bug
Declaring the target scope using an array not supported as per the bicep spec

Azure Policy Documentation "Azure Policy Definition deployments target either subscription or management group scopes."

To Reproduce
Add the following to a Bicep file containing a Policy Definition:

targetScope = [
  'managementGroup'
  'subscription'
]

VS Code Warning

Expected a value of type "'managementGroup' | 'resourceGroup' | 'subscription' | 'tenant'" but the provided value is of type "array".bicep(BCP033)

Additional context
Add any other context about the problem here.

[alex-frankel]

Closing as dup of #788, but we should try to take care of this sooner rather than later cc @majastrz / @shenglol FYI