Build script doesn't take into account Cargo's `unstable.allow-features`

[Nemo157]

root@8671a3d656bc:/# cargo new foo
    Creating binary (application) `foo` package
note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

root@8671a3d656bc:/# cd foo

root@8671a3d656bc:/foo# mkdir .cargo

root@8671a3d656bc:/foo# echo 'unstable.allow-features = []' > .cargo/config.toml

root@8671a3d656bc:/foo# cargo add io-extras
    Updating crates.io index
      Adding io-extras v0.19.0 to dependencies
             Features:
             - async-std
             - mio
             - os_pipe
             - socket2
             - tokio
             - use_async_std
             - use_mio_net
             - use_mio_os_ext
             - use_os_pipe
             - use_socket2
             - use_tokio
    Updating crates.io index
     Locking 13 packages to latest Rust 1.96.0 compatible versions

root@8671a3d656bc:/foo# cargo +nightly check
  Downloaded io-lifetimes v3.0.1
  Downloaded io-extras v0.19.0
  Downloaded 2 crates (62.1KiB) in 0.14s
   Compiling io-lifetimes v3.0.1
   Compiling io-extras v0.19.0
error[E0725]: the feature `can_vector` is not in the list of allowed features
  --> /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/io-extras-0.19.0/src/lib.rs:19:33
   |
19 | #![cfg_attr(can_vector, feature(can_vector))]
   |                                 ^^^^^^^^^^

AFAICT there is no way to disable nightly-detection in this crate making it impossible to use in projects that use nightly but explicitly restrict unstable features.