gimp-with-plugins: Use consistent GIMP version

In case `gimp` attribute from `gimpPlugins` scope is overridden to something different than the top-level one.

pkgs/applications/graphics/gimp/wrapper.nix

···
-{ lib, symlinkJoin, gimp, makeWrapper, gimpPlugins, gnome, plugins ? null}:
+{ lib, symlinkJoin, makeWrapper, gimpPlugins, gnome, plugins ? null}:
 
 let
+inherit (gimpPlugins) gimp;
 allPlugins = lib.filter (pkg: lib.isDerivation pkg && !pkg.meta.broken or false) (lib.attrValues gimpPlugins);
-selectedPlugins = lib.filter (pkg: pkg != gimpPlugins.gimp) (if plugins == null then allPlugins else plugins);
+selectedPlugins = lib.filter (pkg: pkg != gimp) (if plugins == null then allPlugins else plugins);
 extraArgs = map (x: x.wrapArgs or "") selectedPlugins;
 versionBranch = lib.versions.majorMinor gimp.version;