Reorder test lint settings to ignore unknown rust-2024-compatibility …

…in old rustc

The `allow(unknown_lints)` applies only to attributes that come after it.

    warning: unknown lint: `rust_2024_compatibility`
     --> tests/distributed_slice.rs:2:9
      |
    2 | #![deny(rust_2024_compatibility, unsafe_op_in_unsafe_fn)]
      |         ^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean: `rust_2021_compatibility`
      |
      = note: `#[warn(unknown_lints)]` on by default

tests/distributed_slice.rs

@@ -1,6 +1,6 @@
 #![cfg_attr(feature = "used_linker", feature(used_with_arg))]
-#![deny(rust_2024_compatibility, unsafe_op_in_unsafe_fn)]
 #![allow(unknown_lints, non_local_definitions)] // FIXME
+#![deny(rust_2024_compatibility, unsafe_op_in_unsafe_fn)]
 
 use linkme::distributed_slice;
 use once_cell::sync::Lazy;