patch 8.1.0280: 'incsearch' highlighting does not work for ":g!/"

Problem:    'incsearch' highlighting does not work for ":g!/".
Solution:   Skip the exclamation mark. (Hirohito Higashi)
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index 05046b3..8d4b7cc 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -399,6 +399,14 @@
   undo
   call feedkeys(":global/the\<c-l>/d\<cr>", 'tx')
   call assert_equal('  3 the theother', getline(2))
+  undo
+  call feedkeys(":g!/the\<c-l>/d\<cr>", 'tx')
+  call assert_equal(1, line('$'))
+  call assert_equal('  2 the~e', getline(1))
+  undo
+  call feedkeys(":global!/the\<c-l>/d\<cr>", 'tx')
+  call assert_equal(1, line('$'))
+  call assert_equal('  2 the~e', getline(1))
 
   call Incsearch_cleanup()
 endfunc