Reenable AIX in CI

[Thomasdezeeuw]

Currently std lib doesn't build:

  error[E0425]: cannot find function `getenv` in this scope
     --> /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/pal/unix/os.rs:285:22
      |
  285 |     if let Some(p) = getenv(OsStr::from_bytes("PATH".as_bytes())) {
      |                      ^^^^^^ not found in this scope
      |
  help: consider importing one of these functions
      |
  8   + use crate::sys::env::getenv;
      |
  8   + use libc::getenv;
      |
  
  For more information about this error, try `rustc --explain E0425`.
  error: could not compile `std` (lib) due to 1 previous error

Depends on rust-lang/rust#141543

[Darksonn]

You should file a bug with rust-lang about this.

[Thomasdezeeuw]

Depends on rust-lang/rust#141543.