rename test files to snake_case

[senekor]

stacked on #2035

[ellnix]

A quick fd reveals these are the only Rust files with dashes in them:

exercises/practice/macros/tests/invalid/comma-sep.rs
exercises/practice/macros/tests/invalid/double-commas.rs
exercises/practice/macros/tests/invalid/leading-comma.rs
exercises/practice/macros/tests/invalid/missing-argument.rs
exercises/practice/macros/tests/invalid/no-comma.rs
exercises/practice/macros/tests/invalid/only-arrow.rs
exercises/practice/macros/tests/invalid/only-comma.rs
exercises/practice/macros/tests/invalid/single-argument.rs
exercises/practice/macros/tests/invalid/triple-arguments.rs
exercises/practice/macros/tests/invalid/two-arrows.rs

We can let them be, or fix them. I don't mind in any case.

I'll do a few tests on the tooling and probably approve.

[senekor]

good catch, gonna fix those

[ellnix]

Can't find anything wrong with it. LGTM!