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_terminal.vim b/src/testdir/test_terminal.vim
index c398bb0..d325f19 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -1453,7 +1453,7 @@
   call assert_fails("call term_dumpwrite({}, 'Xtest.dump')", 'E728:')
   let buf = RunVimInTerminal('', {})
   call TermWait(buf)
-  call assert_fails("call term_dumpwrite(buf, 'Xtest.dump', '')", 'E715:')
+  call assert_fails("call term_dumpwrite(buf, 'Xtest.dump', '')", 'E1206:')
   call assert_fails("call term_dumpwrite(buf, [])", 'E730:')
   call writefile([], 'Xtest.dump')
   call assert_fails("call term_dumpwrite(buf, 'Xtest.dump')", 'E953:')