patch 9.0.0335: checks for Dictionary argument often give a vague error

Problem:    Checks for Dictionary argument often give a vague error message.
Solution:   Give a useful error message. (Yegappan Lakshmanan, closes #11009)
diff --git a/src/testdir/test_charsearch.vim b/src/testdir/test_charsearch.vim
index 06b8ff6..142e6c8 100644
--- a/src/testdir/test_charsearch.vim
+++ b/src/testdir/test_charsearch.vim
@@ -39,7 +39,7 @@
   call setcharsearch({'char' : ''})
   call assert_equal('', getcharsearch().char)
 
-  call assert_fails("call setcharsearch([])", 'E715:')
+  call assert_fails("call setcharsearch([])", 'E1206:')
   enew!
 endfunc