patch 8.0.0585: test_options fails when run in the GUI

Problem:    Test_options fails when run in the GUI.
Solution:   Also check the 'imactivatekey' value when the GUI is not running.
            Specify test values that work and that fail.
diff --git a/src/testdir/gen_opt_test.vim b/src/testdir/gen_opt_test.vim
index b69ae67..019c757 100644
--- a/src/testdir/gen_opt_test.vim
+++ b/src/testdir/gen_opt_test.vim
@@ -96,6 +96,7 @@
       \ 'guifontwide': [['', 'fixedsys'], []],
       \ 'helplang': [['', 'de', 'de,it'], ['xxx']],
       \ 'highlight': [['', 'e:Error'], ['xxx']],
+      \ 'imactivatekey': [['', 'S-space'], ['xxx']],
       \ 'isfname': [['', '@', '@,48-52'], ['xxx', '@48']],
       \ 'isident': [['', '@', '@,48-52'], ['xxx', '@48']],
       \ 'iskeyword': [['', '@', '@,48-52'], ['xxx', '@48']],