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_functions.vim b/src/testdir/test_functions.vim
index b17a60d..971be40 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -2294,7 +2294,7 @@
   endfunction
   let mydict = {'data': [0, 1, 2, 3], 'len': function("Mylen")}
   eval mydict.len->call([], mydict)->assert_equal(4)
-  call assert_fails("call call('Mylen', [], 0)", 'E715:')
+  call assert_fails("call call('Mylen', [], 0)", 'E1206:')
   call assert_fails('call foo', 'E107:')
 
   " These once caused a crash.