add CI job to test tftpboot

tests/tftpboot/configuration.nix

@@ -0,0 +1,33 @@
+{ config, pkgs, lib, lim, ... } :
+let
+  inherit (pkgs.pseudofile) dir symlink;
+  dts = pkgs.runCommand "qemu.dts" {
+    nativeBuildInputs = with pkgs.pkgsBuildBuild; [ dtc qemu ];
+  } ''
+      qemu-system-arm -machine virt -machine dumpdtb=tmp.dtb
+      dtc -I dtb -O dts -o $out tmp.dtb
+    '';
+in {
+  imports = [
+    ../../modules/outputs/ext4fs.nix
+    ../../modules/outputs/tftpboot.nix
+  ];
+  config = {
+    hardware.dts.src = lib.mkForce dts;
+    boot.tftp = {
+      loadAddress = lim.parseInt "0x42000000";
+      serverip = "10.0.2.2";
+      ipaddr = "10.0.2.15";
+    };
+    boot.imageFormat = "fit";
+    rootfsType = "ext4";
+    filesystem = dir {
+      hello = {
+        type = "f";
+        uid = 7;
+        gid = 24;
+        file = "hello world";
+      };
+    };
+  };
+}