issue2md: add ldflags

Context: 
- https://github.com/NixOS/nixpkgs/pull/456918#discussion_r2479429015
- https://github.com/NixOS/nixpkgs/issues/346380

pkgs/by-name/is/issue2md/package.nix

@@ -17,6 +17,10 @@ buildGoModule (finalAttrs: {
 
   vendorHash = null;
 
+  ldflags = [
+    "-s"
+  ];
+
   meta = {
     description = "CLI tool to convert GitHub issue into Markdown file";
     homepage = "https://github.com/bigwhite/issue2md";