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_search_stat.vim b/src/testdir/test_search_stat.vim
index e0820e4..71e050c 100644
--- a/src/testdir/test_search_stat.vim
+++ b/src/testdir/test_search_stat.vim
@@ -259,7 +259,7 @@
 endfunc
 
 func Test_searchcount_fails()
-  call assert_fails('echo searchcount("boo!")', 'E715:')
+  call assert_fails('echo searchcount("boo!")', 'E1206:')
   call assert_fails('echo searchcount({"timeout" : []})', 'E745:')
   call assert_fails('echo searchcount({"maxcount" : []})', 'E745:')
   call assert_fails('echo searchcount({"pattern" : []})', 'E730:')