Cleanup: Add missing BLI headers.

Not sure why I got an error about this today in one of my usual
builds... very mysterious, but the `BLI_array_utils.hh` include does
seem to be missing anyway.

source/blender/nodes/geometry/nodes/node_geo_curves_to_grease_pencil.cc

@@ -2,6 +2,8 @@
  *
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
+#include "BLI_array_utils.hh"
+
 #include "BKE_curves.hh"
 #include "BKE_grease_pencil.hh"
 #include "BKE_instances.hh"

source/blender/nodes/geometry/nodes/node_geo_grease_pencil_to_curves.cc

@@ -2,6 +2,8 @@
  *
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
+#include "BLI_array_utils.hh"
+
 #include "BKE_curves.hh"
 #include "BKE_grease_pencil.hh"
 #include "BKE_instances.hh"