mamba: mark as broken

Failing Hydra build: https://hydra.nixos.org/build/230518081

So apparently `vasprintf`, `asprintf` are now available by default, not
just with `_GNU_SOURCE` and now `mamba` (or to be precise, its
dependency `xputty`) fails like this:

    ../xputty/xfilepicker.c:225:5: error: format not a string literal and no format arguments [-Werror=format-security]
      225 |     asprintf(&filepicker->path, path);
          |     ^~~~~~~~

It seems as if now that these functions are available by default, the
format-security check from gcc actually works.

pkgs/applications/audio/mamba/default.nix

@@ -37,5 +37,8 @@ stdenv.mkDerivation rec {
     license = licenses.bsd0;
     maintainers = with maintainers; [ magnetophon orivej ];
     platforms = platforms.linux;
+    # 2023-08-19, `-Werror=format-security` fails for xputty
+    # reported as https://github.com/brummer10/libxputty/issues/12
+    broken = true;
   };
 }