Update flake.nix with aarch64

flake.nix

@@ -11,12 +11,14 @@
   inputs.overlay-tool.flake = false;
   inputs.flake-compat.url = "github:edolstra/flake-compat";
   inputs.flake-compat.flake = false;
-  outputs = sources@{nixpkgs, ...}: 
-  let 
-    system = "x86_64-linux";
-    env = import ./ci/default.nix { inherit sources; nixpkgs = nixpkgs.legacyPackages."${system}"; };
+  outputs = sources@{nixpkgs, ...}:
+  let
+    env_x86 = import ./ci/default.nix { inherit sources; nixpkgs = nixpkgs.legacyPackages."x86_64-linux"; };
+    env_aarch64 = import ./ci/default.nix { inherit sources; nixpkgs = nixpkgs.legacyPackages."aarch64-linux"; };
   in {
-    devShells."${system}".default = env;
-    hydraJobs.env."${system}" = env;
+    devShells."x86_64-linux".default = env_x86;
+    devShells."aarch64-linux".default = env_aarch64;
+    hydraJobs.env."x86_64-linux" = env_x86;
+    hydraJobs.env."aarch64-linux" = env_aarch64;
   };
 }