Should "adminusername-should-not-be-literal" also apply to indirectly through a variable?

Uche:
> It's not clear that a variable is bad for adminUserName, "instead use a parameter"

Current behavior is that this fails the test:
```bicep
var adminUsername = 'hello'

resource vm 'Microsoft.Compute/virtualMachines@2020-12-01' = {
name: 'name'
location: resourceGroup().location
properties: {
osProfile: {
adminUsername: adminUsername
}
}
}
```

Start by reproducing the shown Bicep snippet and locating the implementation and tests for the "adminusername-should-not-be-literal" rule. Confirm whether indirect values through variables should be accepted or rejected; done means the rule and its test coverage reflect that decision.

Written by the indexing model from the issue text.