OpenTofu potential leaking of secret variable values when using static evaluation in v1.8

Summary

### Impact Users who have opted into static evaluation of module sources, versions, and backend configurations may be at risk of exposing sensitive variables and locals. This is a workflow that should not be possible and explicitly show errors. ### Workarounds Check that you are not using sensitive variables in module sources and versions, as well as backend configurations. The patch will add explicit errors and prevent this from being possible. ### Examples ```hcl variable "backend_path" { type = string sensitive = true } terraform { backend "local" { path = var.backend_path } } ``` ```hcl variable "mod_info" { type = string sensitive = true } module "foo" { source = var.mod_info //version = var.mod_info } ```