Ruby 3.1: Add specs for `Time#new` `in` keyword

[ohbarye]

Issue

• Write specs for new Ruby 3.1 features and changes #923

Change

This pull request covers the spec below.

• [ ] Time.new now accepts optional in: keyword argument for the timezone, as well as Time.at and Time.now, so that is now you can omit minor arguments to Time.new. [Feature #17485]

  Time.new(2021, 12, 25, in: "+07:00")
  #=> 2021-12-25 00:00:00 +0700
  

  At the same time, time component strings are converted to integers more strictly now.

  Time.new(2021, 12, 25, "+07:30")
  #=> invalid value for Integer(): "+07:30" (ArgumentError)
  

  Ruby 3.0 or earlier returned probably unexpected result 2021-12-25 07:00:00, not 2021-12-25 07:30:00 nor 2021-12-25 00:00:00 +07:30.

I used test cases for Time.at as a reference.

[eregon]

Thank you, could you also add specs for Time.at(..., in:) and Time.now(in: ) since that's part of the same item?

[ohbarye]

Sure thing. How about fe751cb and 6b1c28a?

[ohbarye]

Thank you too!