[gnome-applets/wip/muktupavels/werror] trash: fix -Wsuggest-attribute=format warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit a0bd472a35aa4429802a5a03619d248a87d210e9
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sat Apr 4 22:50:58 2020 +0300

    trash: fix -Wsuggest-attribute=format warning

 gnome-applets/trash/trash-applet.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/gnome-applets/trash/trash-applet.c b/gnome-applets/trash/trash-applet.c
index 22fa4f4cc..243963f86 100644
--- a/gnome-applets/trash/trash-applet.c
+++ b/gnome-applets/trash/trash-applet.c
@@ -278,6 +278,11 @@ trash_applet_drag_motion (GtkWidget      *widget,
   return TRUE;
 }
 
+static void
+error_dialog (TrashApplet *applet,
+              const gchar *error,
+              ...) G_GNUC_PRINTF (2, 3);
+
 /* TODO - Must HIGgify this dialog */
 static void
 error_dialog (TrashApplet *applet, const gchar *error, ...)