Incomplete type checking on object indexers

[afscrome]

Bicep version
run bicep --version via the Bicep CLI, az bicep version via the AZ CLI or via VS code by navigating to the extensions tab and searching for Bicep

Describe the bug
When indexing into an object with a string property, type checking doesn't seem to be fully done. In the below repo steps, foo the indexer should allow values of type 'One' | 'Two', and Input is of type 'Three' | 'Four'. There is no way that foo[Input] could ever succeed, so I'd expect the following code to result in a compiler error as there's no way this could result in anything other than a failure

To Reproduce

@allowed([
  'Three'
  'Four'
])
param Input string

var foo = {
  One: 'Hello'
  Two: 'World'
}

var x = foo[Input]

Additional context
A more interesting variant is when there is the types partially match. (e.g. what if Input was of type 'Two' | 'Three' | 'Four'.) should this continue to be an error, or should it be a warning instead?