rtk: fix build with Rust 1.97

Rust 1.97 exposes dead code while compiling rtk 0.43.0's test target, and upstream promotes warnings to errors.

Cap lints until a release includes the develop-branch fix from https://github.com/rtk-ai/rtk/commit/73b8cb3069297374a3de58552b9fe4aa2cda3a41.

pkgs/by-name/rt/rtk/package.nix

@@ -24,6 +24,12 @@ rustPlatform.buildRustPackage (finalAttrs: {
 
   cargoHash = "sha256-XKUKdhxfnwUCOx9slqx4oUFa09HcosPLVh5Xkh87oSk=";
 
+  # Rust 1.97's dead_code_pub_in_binary analysis exposes dead code in test builds.
+  # Fixed upstream on develop after 0.43.0:
+  # https://github.com/rtk-ai/rtk/commit/73b8cb3069297374a3de58552b9fe4aa2cda3a41
+  # TODO: Remove RUSTFLAGS when updating rtk to the next release.
+  env.RUSTFLAGS = "--cap-lints warn";
+
   nativeBuildInputs = [
     makeWrapper
     pkg-config