ci: use beta, add secondary nightly ci.

examples/nrf5340/src/bin/blinky.rs

@@ -1,6 +1,5 @@
 #![no_std]
 #![no_main]
-#![feature(type_alias_impl_trait)]
 
 use embassy_executor::Spawner;
 use embassy_nrf::gpio::{Level, Output, OutputDrive};

examples/nrf5340/src/bin/gpiote_channel.rs

@@ -1,6 +1,5 @@
 #![no_std]
 #![no_main]
-#![feature(type_alias_impl_trait)]
 
 use defmt::info;
 use embassy_executor::Spawner;

examples/nrf5340/src/bin/uart.rs

@@ -1,6 +1,5 @@
 #![no_std]
 #![no_main]
-#![feature(type_alias_impl_trait)]
 
 use defmt::*;
 use embassy_executor::Spawner;