bump: rust version to nightly-2024-09-21

rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
-channel = "nightly-2024-04-27"
+channel = "nightly-2024-09-21"
 components = ["rustfmt", "llvm-tools-preview"]
 targets = ["riscv64imac-unknown-none-elf"]
 profile = "minimal"