gnu: g-golf-adw-1-examples: Fix build.

Environment variable GDK_PIXBUF_MODULE_FILE is no longer set since
4838b7b0e9.
See <https://bugs.gnu.org/76697#10>.

* gnu/packages/guile-xyz.scm (g-golf-adw-1-examples)[arguments]: Actually
use GLIB-OR-GTK-BUILD-SYSTEM’s phases, which set the GDK_PIXBUF_MODULE_FILE
environment variable.

Change-Id: Ib2a7036833360ef265f3a6a368498cf6aabf9b08

gnu/packages/guile-xyz.scm

@@ -2878,7 +2878,10 @@ writing a Guix package.")))
       #:phases
       (with-imported-modules `((guix build guile-build-system)
                                ,@%default-gnu-imported-modules)
-        #~(modify-phases %standard-phases
+        ;; With above modules, %standard-phases would not be from
+        ;; glib-or-gtk-build-system anymore:
+        #~(modify-phases (@ (guix build glib-or-gtk-build-system)
+                            %standard-phases)
             (add-after 'unpack 'prepare-examples
               (lambda _
                 (chdir "examples/adw-1")