patch 9.0.1148: cmdline test fails in the GUI

Problem:    Cmdline test fails in the GUI.
Solution:   Skip the test when running in the GUI.
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 91ff6f1..a832306 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -655,6 +655,9 @@
 endfunc
 
 func Test_multibyte_expression()
+  " Get a dialog in the GUI
+  CheckNotGui
+
   " This was using uninitialized memory.
   let lines =<< trim END
       set verbose=6