Add Ruby-4

[mbj]

No description provided.

[sferik]

I noticed a random test failure in your branch, despite it passing in my branch.

I believe this is due to the fact that, in Ruby 4.0, read_nonblock with exception: false can return :wait_readable even after select indicates readability (spurious wakeup). I believe we could catch the when :wait_readable case here and return false:

mutant/ruby/lib/mutant/parallel/connection.rb

Lines 117 to 133 in a0413a2

	def with_nonblock_read(io:, max_bytes:)
	io.binmode
	chunk = io.read_nonblock(max_bytes, exception: false)
	case chunk
	when nil
	@errors << EOFError
	false
	when String
	yield chunk
	else
	fail "Unexpected nonblocking read return: #{chunk.inspect}"
	end
	end
	# rubocop:enable Metrics/MethodLength
	end

Let me know what you think of this approach and I can push up another commit.