gtkfilechooserwidget: Mark string as no-c-format

gettext 0.22 recognizes %b as a C string format which
not is true for date strings, so explicitly mark as
no-c-format.

gtk/gtkfilechooserwidget.c

@@ -3774,6 +3774,7 @@ my_g_format_date_for_display (GtkFileChooserWidget *impl,
     }
   else if (g_date_time_get_year (now) == g_date_time_get_year (time))
     {
+      /* xgettext:no-c-format */
       format = _("%-e %b");
     }
   else