`validateExpressions()` incorrectly reports `UnknownVariable` when indices are used within expressions

[danlevison]

Describe the bug
When using [i]. syntax, the validateExpressions() returns a type 2 error.

Steps to reproduce

See demo - https://codesandbox.io/p/devbox/shy-rain-tm4rm8?workspaceId=ws_UBrjJL1E93iKDqX3Nj8Spq

Expected behavior
validateExpressions() should not return an error here