add gitbug

shell.nix

···
   default = pkgs.mkShell {
     # Enable experimental features without having to specify the argument
     NIX_CONFIG = "experimental-features = nix-command flakes";
-    nativeBuildInputs = with pkgs; [ nix home-manager git agenix deploy-rs dnscontrol ];
+    nativeBuildInputs = with pkgs; [
+      nix
+      home-manager
+      git
+      agenix
+      deploy-rs
+      dnscontrol
+      git-bug
+    ];
   };
 }