Include snippet related to conditional compilation in documentation listings

[integraledelebesgue]

Which component is the issue related to?

Foundry Book

Issue

At the moment, code from docs/listings/snforge_advanced_features/crates/conditional_compilation/src/function.cairo is not being tested. Line declaring it as a module is commented.

Even though both function and its test module are compiled conditionally, compilation fails with an error:

error: Function not found.
 --> [...]/starknet-foundry/docs/listings/snforge_advanced_features/crates/conditional_compilation/src/function.cairo:9:1
    #[test]
^*********^

@maciektr explained that a bug in Scarb causing this has been solved here.

We need to include this file as soon as Foundry starts using newer Scarb in the future.