Example usage of test_matrix broken

[till-metaco]

Description

The example usage for test_matrix does not compile in version 3.3.1 with rustc 1.77.2.

To reproduce

1. Create an empty project with cargo new test_matrix
2. Add test_case with cargo add --dev test-case
3. Add the test module from the example usage on crates.io like so

   
   fn main() {
   println!("Hello, world!");
   }

[cfg(test)]

mod tests { use test_case::test_matrix;

#[test_matrix(
    [-2, 2],
    [-4, 4]
)]
fn multiplication_matrix_tests(x: i8, y: i8) {
    let actual = (x * y).abs();

    assert_eq!(8, actual)
}

}

4. Compile and run the tests with `cargo test`

## Expected behaviour

The tests compile and run without errors

## Actual behaviour

The tests don't compile with the error message

error[E0428]: the name _2_2_expects is defined multiple times --> src/main.rs:9:5	9	/ #[test_matrix( 10		[-2, 2], 11		[-2, 4] 12		)]		__^ _2_2_expects redefined here

= note: _2_2_expects must be defined only once in the value namespace of this module = note: this error originates in the attribute macro test_matrix (in Nightly builds, run with -Z macro-backtrace for more info)

## Additional context

The error seems to stem from the way the minus signs are translated to function names, because it compiles if the matrix is defined as

```rust
   #[test_matrix(
        [-1, 2],
        [-3, 4]
    )]

(these tests compile, but fail for obvious reasons.

[till-metaco]

Seems related to #19