Extend `maybe_misused_cfg` to cover `#[cfg(tests)]`

[SabrinaJewson]

Description

An easy misspelling to make is to write something like:

pub fn add(left: usize, right: usize) -> usize {
    left + right
}

#[cfg(tests)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        let result = add(2, 2);
        assert_eq!(result, 4);
    }
}

This will not result in any warnings or errors currently, but will simply not run any of the tests. Clippy should instead output a warning:

warning: test may misspelled as tests
 --> src/lib.rs:5:7
  |
5 | #[cfg(tests)]
  |       ^^^^^ help: use: `test`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/
index.html#maybe_misused_cfg
  = note: `#[warn(clippy::maybe_misused_cfg)]` on by default

Version

rustc 1.71.0 (8ede3aae2 2023-07-12)
binary: rustc
commit-hash: 8ede3aae28fe6e4d52b38157d7bfe0d3bceef225
commit-date: 2023-07-12
host: x86_64-unknown-linux-gnu
release: 1.71.0
LLVM version: 16.0.5

Additional Labels

@rustbot label +C-enhancement

[SabrinaJewson]

Another thing to add to this, since I just saw someone accidentally do it: #[cfg(Test)] and other alternately-cased misspellings.