ruff: add emulatorAvailable check

pkgs/by-name/ru/ruff/package.nix

@@ -35,7 +35,7 @@ rustPlatform.buildRustPackage (finalAttrs: {
     rust-jemalloc-sys
   ];
 
-  postInstall =
+  postInstall = lib.optionalString (stdenv.hostPlatform.emulatorAvailable buildPackages) (
     let
       emulator = stdenv.hostPlatform.emulator buildPackages;
     in
@@ -44,7 +44,8 @@ rustPlatform.buildRustPackage (finalAttrs: {
         --bash <(${emulator} $out/bin/ruff generate-shell-completion bash) \
         --fish <(${emulator} $out/bin/ruff generate-shell-completion fish) \
         --zsh <(${emulator} $out/bin/ruff generate-shell-completion zsh)
-    '';
+    ''
+  );
 
   # Run cargo tests
   checkType = "debug";