Explicitly run +nightly for -Zcheck-cfg pass in ci.

[targrub]

Objective

Getting this error running ci locally.

$ cargo check -Zcheck-cfg --workspace
error: the `-Z` flag is only accepted on the nightly channel of Cargo, but this is the `stable` channel
See https://doc.rust-lang.org/book/appendix-07-nightly-rust.html for more information about Rust release channels.
thread 'main' panicked at tools\ci\src\main.rs:166:14:
Please fix failing cfg checks in output above.: command exited with non-zero code `cargo check -Zcheck-cfg --workspace`: 101

Solution

• Add +nightly flag to the check-cfg pass.

---

Obviously we shouldn't be running nightly Cargo, but at least now local running of cargo run -p ci will pass.

[rparrett]

I am seeing this output locally:

 cargo run -p ci cfg-check
    Blocking waiting for file lock on build directory
   Compiling ci v0.1.0 (/Users/me/src/bevy/tools/ci)
    Finished dev [unoptimized + debuginfo] target(s) in 13.70s
     Running `target/debug/ci cfg-check`
$ cargo check +nightly -Zcheck-cfg --workspace
error: unexpected argument '+nightly' found

[targrub]

Note: The PR for cfg-check was #12103.

[BD103]

Perhaps in the future it would be nice to check whether CI is being compiled from a nightly toolchain or not (I'm thinking build.rs or env!?), to dynamically skip check-cfg.

[targrub]

... previous cargo run -p ci output
...
$ cargo +nightly check -Zcheck-cfg --workspace
error: no such command: `+nightly`

        Cargo does not handle `+toolchain` directives.
        Did you mean to invoke `cargo` through `rustup` instead?
thread 'main' panicked at tools\ci\src\main.rs:166:14:
Please fix failing cfg checks in output above.: command exited with non-zero code `cargo +nightly check -Zcheck-cfg --workspace`: 101

That's what I get from cargo run -p ci. But if I run cargo +nightly check -Zcheck-cfg --workspace separately, it works.