Add release notes for 1.85.1

Author: cuviper

RELEASES.md

@@ -1,3 +1,14 @@
+Version 1.85.1 (2025-03-18)
+==========================
+
+<a id="1.85.1"></a>
+
+- [Fix the doctest-merging feature of the 2024 Edition.](https://github.com/rust-lang/rust/pull/137899/)
+- [Relax some `target_feature` checks when generating docs.](https://github.com/rust-lang/rust/pull/137632/)
+- [Fix errors in `std::fs::rename` on Windows 1607.](https://github.com/rust-lang/rust/pull/137528/)
+- [Downgrade bootstrap `cc` to fix custom targets.](https://github.com/rust-lang/rust/pull/137460/)
+- [Skip submodule updates when building Rust from a source tarball.](https://github.com/rust-lang/rust/pull/137338/)
+
 Version 1.85.0 (2025-02-20)
 ==========================