Correctness test for custom data types show validation issues

[ghaith]

Describe the bug
The correctness test 'custom_datatypes.rs" shows a validation error but passes
It looks like the variable reference is not being resolved correctly

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Running tests/tests.rs (target/debug/deps/tests-f27738ba36930a8b)

running 1 test
error: Could not resolve reference to 'i
   ┌─ external_test.st:18:19
   │
18 │         data.arr1[i] := i;
   │                   ^

error: Could not resolve reference to 'i
   ┌─ external_test.st:19:19
   │
19 │         data.arr2[i] := i*10;
   │                   ^

test correctness::custom_datatypes::using_inline_arrays_in_structs ... ok

[ghaith]

The latest commit fixes the issues with the original tests
However the following tests still show errors:
File: tests/correctness/initial_values.rs
initialization_of_complex_struct_instance
initialization_of_complex_struct_instance_using_defaults
Both show the error : Unresolved constant a

[riederm]

until this is fixed it's woth to redirect std-err to /dev/null
cargo insta test 2> /dev/null

[ghaith]

Validation messages are hidden by the null diagnostian in the runner.rs module

[99NIMI]

We need to re-evaluate this