Auto merge of #120676 - Mark-Simulacrum:bootstrap-bump, r=clubby789

Bump bootstrap compiler to just-built 1.77 beta

https://forge.rust-lang.org/release/process.html#master-bootstrap-update-t-2-day-tuesday

Author: bors

src/lib.rs

@@ -10,7 +10,7 @@
 #![feature(nonzero_ops)]
 #![feature(let_chains)]
 #![feature(lint_reasons)]
-#![cfg_attr(not(bootstrap), feature(trait_upcasting))]
+#![feature(trait_upcasting)]
 // Configure clippy and other lints
 #![allow(
     clippy::collapsible_else_if,