Try this

.woodpecker/.build.yml

@@ -8,6 +8,7 @@ steps:
       # Test
       - nix develop --command dotnet test
       - nix develop --command dotnet test --configuration Release
+      - nix develop --command alejandra --check .
 
     when:
       - event: "push"

flake.nix

@@ -1,26 +1,45 @@
 {
-    description = "Advent of Code 2023";
-    inputs = {
-        flake-utils.url = "github:numtide/flake-utils";
-        nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    };
+  description = "Advent of Code 2023";
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
 
-    outputs = {
-        self,
-        nixpkgs,
-        flake-utils,
-    }: flake-utils.lib.eachDefaultSystem (system:
-    let pkgs = nixpkgs.legacyPackages.${system}; in
-    {
-        devShells = { default = pkgs.mkShell {
-          buildInputs = with pkgs; [
-            (with dotnetCorePackages;
-              combinePackages [
-                dotnet-sdk_8
-                dotnetPackages.Nuget
-              ])
-          ] ++ [pkgs.swift darwin.apple_sdk.frameworks.Foundation darwin.apple_sdk.frameworks.CryptoKit darwin.apple_sdk.frameworks.GSS pkgs.zlib pkgs.zlib.dev pkgs.openssl pkgs.icu];
-        };};
-    }
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+  }:
+    flake-utils.lib.eachDefaultSystem (
+      system: let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+        # Conditionally include Swift and Apple SDK for Darwin systems
+        let
+          darwinDeps =
+            if system == "x86_64-darwin" || system == "aarch64-darwin"
+            then [
+              pkgs.swift
+              pkgs.darwin.apple_sdk.frameworks.Foundation
+              pkgs.darwin.apple_sdk.frameworks.CryptoKit
+              pkgs.darwin.apple_sdk.frameworks.GSS
+            ]
+            else [];
+        in {
+          devShells = {
+            default = pkgs.mkShell {
+              buildInputs = with pkgs;
+                [
+                  (with dotnetCorePackages;
+                    combinePackages [
+                      dotnet-sdk_8
+                      dotnetPackages.Nuget
+                    ])
+                ]
+                ++ darwinDeps
+                ++ [pkgs.zlib pkgs.zlib.dev pkgs.openssl pkgs.icu pkgs.alejandra];
+            };
+          };
+        }
     );
 }