Bring up Rust lang #37612 as a known problem for let_and_return

clippy_lints/src/returns.rs

@@ -25,6 +25,12 @@
     /// It is just extraneous code. Remove it to make your code
     /// more rusty.
     ///
+    /// ### Known problems
+    /// In the case of some temporaries, e.g. locks, eliding the variable binding could lead
+    /// to deadlocks. See [rust-lang issue 37612](https://github.com/rust-lang/rust/issues/37612).
+    /// This could become relevant if the code is later changed to use the code that would have been
+    /// bound without first assigning it to a let-binding.
+    ///
     /// ### Example
     /// ```rust
     /// fn foo() -> String {