gitattributes: disable merge=union in all-packages

This would lead to some merge issues occasionally.

Changed files
+1 -1
+1 -1
.gitattributes
···
nixos/doc/default.nix linguist-documentation=false
nixos/modules/module-list.nix merge=union
-
pkgs/top-level/all-packages.nix merge=union
+
# pkgs/top-level/all-packages.nix merge=union