Use fully qualified #[test] attribute path

[alanbriolat]

I found that uses of #[test_case] fail to build when a different procedural macro attribute is imported with the name test. For example, the simple test code:

#[cfg(test)]
mod tests {
    use test_case::test_case;
    use test_log::test;

    #[test_case("hello, world")]
    fn test_something(s: &str) {
        assert_eq!(s, "hello, world");
    }
}

results in the build error:

error[E0659]: `test` is ambiguous
   --> (REDACTED)
    |
265 |     #[test_case("hello, world")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ambiguous name
    |
    = note: ambiguous because of a conflict between a name from a glob import and an outer scope during import or macro resolution
note: `test` could refer to the attribute macro imported here
   --> (REDACTED)
    |
265 |     #[test_case("hello, world")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: consider adding an explicit import of `test` to disambiguate
    = help: or use `self::test` to refer to this attribute macro unambiguously
note: `test` could also refer to the attribute macro defined here
   --> /home/alan/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/prelude/mod.rs:129:13
    |
129 |     pub use super::v1::*;
    |             ^^^^^^^^^^^^
    = note: this error originates in the attribute macro `test_case` (in Nightly builds, run with -Z macro-backtrace for more info)

I don't expect test_case to necessarily wrap another test helper, but this import probably shouldn't break it. I looked at a couple of other test attributes (#[test_log::test] and #[tokio::test]) to confirm they use #[::core::prelude::v1::test] instead of #[test] in their generated code to avoid ambiguity, so I think the same approach should probably be applied to #[test_case].

[luke-biel]

Thank you for the contribution :) This is something we definitely overlooked.

It appears that once_cell updated their MSRV. I'm gonna fix master and then notify you that you can rebase.

[luke-biel]

Ok @alanbriolat, CI passes, so all I ask from you is to merge in our master into your changes, it should all pass then and we can finalize this PR :)
Thanks again for contribution

[luke-biel]

Thank you very much, I'll try to release it asap