Fix delegation in ActiveModel::Type.lookup

[eregon]

Summary

• Without the change the new test fails like this:

  Failure:
  ActiveModel::TypeTest#test_registering_a_new_type [test/cases/type_test.rb:21]:
  Expected: #<struct args={}>
    Actual: #<struct args=nil>

• (*args, **kwargs)-delegation is not correct on Ruby 2.7 unless the
  target always accepts keyword arguments (not the case for Struct.new(:args).new).
  See https://eregon.me/blog/2021/02/13/correct-delegation-in-ruby-2-27-3.html

Other Information

Similar to #42266, similar issue, similar fix.

[eregon]

I switched to (...) since that works in this case, and it's already used in Rails.

I also took a quick look at other potential delegation issues in ActiveModel with git grep -P '\*.*,.*\*\*' **/*.rb and that only shows lib/active_model/callbacks.rb which seems mostly OK (the target method expects keyword arguments, although not directly with **).

[p8]

@eregon Does this change require at least Ruby 2.7.3?

[eregon]

@p8 No, 2.7.0 already has (...).
2.7.3 adds support for (leading, arg, ...) which 2.7.0 - 2.7.2 does not have, but that's not used here.

[p8]

@eregon Thanks! That's good to know.