parse.y: raise with numeric ID type

* parse.y (rb_id_attrset): all valid ID types are handled
  properly, raise with numeric ID type which may be broken for
  GCed static symbol.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45766 b2dd03c8-39d4-4d8f-98ff-823fe69b080e