cargo-bisect-rustc: set __structuredAttrs

`nix store make-content-addressed` gives the same output

pkgs/by-name/ca/cargo-bisect-rustc/package.nix

@@ -15,6 +15,8 @@ rustPlatform.buildRustPackage (finalAttrs: {
   pname = "cargo-bisect-rustc";
   version = "0.6.11";
 
+  __structuredAttrs = true;
+
   src = fetchFromGitHub {
     owner = "rust-lang";
     repo = "cargo-bisect-rustc";