Add package for aarch64-darwin

flake.lock previously included a "indirect" reference to nixpkgs.

I am not sure what this means but I added `inputs.nixpkgs` and updated nixpkgs because this old version of nixpkgs didn't have any support for aarch64-darwin at all.

Now on a aarch64-darwin I can type `nix build` and get a working version of agenix.

flake.nix

@@ -1,6 +1,10 @@
 {
   description = "Secret management with age";
 
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-21.11";
+  };
+
   outputs = { self, nixpkgs }:
   let
     agenix = system: nixpkgs.legacyPackages.${system}.callPackage ./pkgs/agenix.nix {};
@@ -19,6 +23,9 @@
     packages."x86_64-darwin".agenix = agenix "x86_64-darwin";
     defaultPackage."x86_64-darwin" = self.packages."x86_64-darwin".agenix;
 
+    packages."aarch64-darwin".agenix = agenix "aarch64-darwin";
+    defaultPackage."aarch64-darwin" = self.packages."aarch64-darwin".agenix;
+
     packages."x86_64-linux".agenix = agenix "x86_64-linux";
     defaultPackage."x86_64-linux" = self.packages."x86_64-linux".agenix;
     checks."x86_64-linux".integration = import ./test/integration.nix {

test/integration.nix

@@ -42,9 +42,9 @@ import "${nixpkgs}/nixos/tests/make-test-python.nix" ({ pkgs, ...}: {
     system1.wait_until_succeeds("pgrep -f 'agetty.*tty1'")
     system1.sleep(2)
     system1.send_key("alt-f2")
-    system1.wait_until_succeeds(f"[ $(fgconsole) = 2 ]")
-    system1.wait_for_unit(f"getty@tty2.service")
-    system1.wait_until_succeeds(f"pgrep -f 'agetty.*tty2'")
+    system1.wait_until_succeeds("[ $(fgconsole) = 2 ]")
+    system1.wait_for_unit("getty@tty2.service")
+    system1.wait_until_succeeds("pgrep -f 'agetty.*tty2'")
     system1.wait_until_tty_matches(2, "login: ")
     system1.send_chars("${user}\n")
     system1.wait_until_tty_matches(2, "login: ${user}")