Fix handling incorrect arguments in test attributes

[kkawula]

Which components does the task require to be changed? (think hard pls)

snforge

Description

For example this snippet would work.

#[test]
#[fork(tomato: "red", url: "http://your.rpc.url", block_number: 123)]
fn test_using_forked_state() {
    // ...
}

But in this scenario snforge should throw an error because tomato isn't a proper argument.