ruby-curses: Emits warning: "rb_safe_level will be removed in Ruby 3.0", affects at least irqtop

This is an issue in ruby-curses, not irqtop. See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=958973

Interestingly this no more happens on Debian Unstable/Testing. This seems to have fixed upstream a few months ago:

commit df3f52a6331f1a47af9933b77311a8650727d8d1
  Author: nagachika <email address hidden>
  Date: 2020-09-29 22:43:25 +0900

    merge revision(s) 996af2ce086249e904b2ce95ab2fcd1de7d757be: [Backport #16345] [Backport #17000]

            Disable deprecation warning by the default [Feature #16345]

            And `-w` option turns it on.

That commit likely made it into ruby 2.7.2, which hit Debian Unstable in mid-October 2020.

Nevertheless this obviously needs to be fixed in ruby-curses.

Note: The cited commit and "fix" was in the package ruby, but the problem in ruby-curses still exists as ruby only silenced the deprecation warnings by default.

Problem does not seem to be solved as now irqtop fails completely.

root@hongkong:~# irqtop
<internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require': /usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/3.0.0/curses.so: undefined symbol: rb_safe_level - /usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/3.0.0/curses.so (LoadError)
 from <internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require'
 from /usr/lib/ruby/vendor_ruby/curses.rb:18:in `rescue in <top (required)>'
 from /usr/lib/ruby/vendor_ruby/curses.rb:14:in `<top (required)>'
 from <internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require'
 from <internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require'
 from /usr/bin/irqtop:9:in `<main>'
<internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require': cannot load such file -- 3.0/curses.so (LoadError)
 from <internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require'
 from /usr/lib/ruby/vendor_ruby/curses.rb:16:in `<top (required)>'
 from <internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require'
 from <internal:/usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_require.rb>:85:in `require'
 from /usr/bin/irqtop:9:in `<main>'

root@hongkong:~# dpkg -l irqtop ruby-curses
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============-=============-============-=============================================
ii irqtop 2.6-2ubuntu1 all Observe IRQ and SoftIRQ in a top-like fashion
ii ruby-curses 1.2.4-1build3 amd64 curses binding for Ruby

root@hongkong:~# cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.1 LTS"