Can't load time with year greater than or equal to 10000

Steps to reproduce

require "psych"
require "time"
require "minitest/autorun"

class YearTenThousandTest < Minitest::Test
  def test_year_ten_thousand
    time = Time.parse("10000-01-01 00:00:00")

    yaml_string = Psych.dump(time)
    yaml_time = Psych.load(yaml_string)

    assert_equal yaml_time, time
  end
end

Expected behavior

Expected Psych.load to return a Time object, like it does for years <= 9999.

Actual behavior

It returns a string.

System configuration

Ruby version: 2.6.1

Originally reported as https://github.com/rails/rails/issues/35783

Reproduce the failure with the YearTenThousandTest example, focusing on Psych.dump and Psych.load with a Time parsed by Time.parse. Trace how Psych decides whether a dumped time is loaded as a Time or String, then add coverage for year >= 10000 and verify the round trip returns a Time object.