add release notes for 1.80.1

Author: pietroalbini

Diff for: RELEASES.md

@@ -1,3 +1,11 @@
+Version 1.80.1 (2024-08-08)
+===========================
+
+<a id="1.80.1"></a>
+
+- [Fix miscompilation in the jump threading MIR optimization when comparing floats](https://github.com/rust-lang/rust/pull/128271)
+- [Revert changes to the `dead_code` lint from 1.80.0](https://github.com/rust-lang/rust/pull/128618)
+
 Version 1.80.0 (2024-07-25)
 ==========================