Update Rust nightly.

Removes feature(generic_associated_types)

examples/boot/application/nrf/src/bin/a.rs

@@ -1,7 +1,6 @@
 #![no_std]
 #![no_main]
 #![macro_use]
-#![feature(generic_associated_types)]
 #![feature(type_alias_impl_trait)]
 
 use embassy_boot_nrf::FirmwareUpdater;

examples/boot/application/nrf/src/bin/b.rs

@@ -1,7 +1,6 @@
 #![no_std]
 #![no_main]
 #![macro_use]
-#![feature(generic_associated_types)]
 #![feature(type_alias_impl_trait)]
 
 use embassy_executor::Spawner;