patch 8.0.0392: GUI test fails with Athena and Motif

Problem:    GUI test fails with Athena and Motif.
Solution:   Add test_ignore_error().  Use it to ignore the "failed to create
            input context" error.
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index 77e4f2e..6c9722d 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -17,6 +17,9 @@
 " Test for resetting "secure" flag after GUI has started.
 " Must be run first.
 func Test_1_set_secure()
+  " Ignore the "failed to create input context" error.
+  call test_ignore_error('E285')
+
   set exrc secure
   gui -f
   call assert_equal(1, has('gui_running'))