bump rb-sys for ruby 4 support

[davekaro]

Fixes #34

[mudge]

Is it worth updating

mrml-ruby/.github/workflows/cross-compile.yml

Line 41 in 4798cc3

ruby-versions: "2.7,3.0,3.1,3.2,3.3,3.4"

too so there is precompiled, native support for Ruby 4.0?

It might also be worth considering dropping some of the older Ruby ABI versions here to save space in the gems (and because I've found versions older than 3.1 to increasingly be a pain to compile in my own gems). Note that rake-compiler-dock 1.11.0 dropped support for Ruby 2.7.

As the Ruby versions seem to be passed to rake-compiler-dock's RakeCompilerDock.ruby_cc_version, this could be simplified to:

ruby-versions: "~> 3.0,~> 4.0"

[davekaro]

Considering Ruby 3.1 has an end-of-life of 2025-03-26, I think it makes sense to drop 2.7 and 3.0, maybe even 3.1. But I'll defer to the maintainers.