scooter: compile only scooter

I was seeing the following error when installing `scooter` after
installing `lsp-ai`. This change specifies the bin `scooter`.

```bash
➜ nix profile add nixpkgs#scooter
error: An existing package already provides the following file:

/nix/store/lzqlq6jrb4rlx6si51xrg3blgcvpn0d9-lsp-ai-0.7.1/bin/xtask

       This is the conflicting file from the new package:

/nix/store/nminr7pl0zd9ikr2xbdbx74lilwcm3bk-scooter-0.5.3/bin/xtask

       To remove the existing package:

         nix profile remove lsp-ai

       The new package can also be added next to the existing one by
assigning a different priority.
       The conflicting packages have a priority of 5.
       To prioritise the new package:

         nix profile add
flake:nixpkgs#legacyPackages.aarch64-darwin.scooter --priority 4

       To prioritise the existing package:

         nix profile add
flake:nixpkgs#legacyPackages.aarch64-darwin.scooter --priority 6
```

pkgs/by-name/sc/scooter/package.nix

@@ -18,6 +18,12 @@ rustPlatform.buildRustPackage rec {
   useFetchCargoVendor = true;
   cargoHash = "sha256-kPweKXAitvODNoKTr2iB+qM9qMWGoKEQCxpkgrpnewY=";
 
+  # Ensure that only the `scooter` package is built (excluding `xtask`)
+  cargoBuildFlags = [
+    "--package"
+    "scooter"
+  ];
+
   # Many tests require filesystem writes which fail in Nix sandbox
   doCheck = false;