dwarf-fortress-packages.dwarf-therapist: disable on AArch64

The game works only on x86 anyway.

pkgs/games/dwarf-fortress/dwarf-therapist/default.nix

···
     description = "Tool to manage dwarves in in a running game of Dwarf Fortress";
     maintainers = with maintainers; [ the-kenny abbradar bendlas ];
     license = licenses.mit;
-    platforms = platforms.linux;
+    platforms = [ "x86_64-linux" "i686-linux" ];
     homepage = https://github.com/Dwarf-Therapist/Dwarf-Therapist;
   };
 }