`Kernel.#fork` failed in child process when fork_mode is parent

[nirareba1969]

Your environment

• ruby -v: ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-linux]
• rdbg -v: rdbg 1.5.0

Describe the bug

Kernel.#fork failed in child process when fork_mode is parent

To Reproduce

Script

require "debug"

DEBUGGER__::CONFIG[:fork_mode] = :parent

fork do
  puts 'parent forked.'
  fork do
    puts 'child forked.'
  end
end

Repository for try easily

https://github.com/nirareba1969/debug-test#for-docker

Expected behavior

DEBUGGER: Detaching after fork from child process 9
parent forked.
child forked.

Actual behavior

DEBUGGER: Detaching after fork from child process 9
parent forked.
/usr/local/bundle/gems/debug-1.5.0/lib/debug/session.rb:2140:in `_fork': no block given (yield) (LocalJumpError)
  from repro.rb:7:in `fork'
  from repro.rb:7:in `block in <main>'
  from repro.rb:5:in `fork'
  from repro.rb:5:in `<main>'

Additional context

None.

[ko1]

Thank you. I can repro.