`make setup-charon` fails with `error[E0554]: #![feature] may not be used on the stable release channel`

[kim-em]

trafficstars

Following the install instructions, at the make setup-charon step (which I had to amend to gmake setup-charon on macos) I get:

error[E0554]: `#![feature]` may not be used on the stable release channel
 --> macros/src/lib.rs:4:1
  |
4 | #![feature(non_exhaustive_omitted_patterns_lint)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0554`.
error: could not compile `macros` (lib) due to 1 previous error

Could you please amend the setup instructions and/or makefile to fix this?