Example usage of test_matrix broken

## 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](https://crates.io/crates/test-case) on crates.io like so
```rust
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.