Fix make_shareable shim in harness-common.rb

[eregon]

Example failure: https://github.com/ruby/ruby-bench/actions/runs/19580397581/job/56076559112#step:4:13

[eregon]

Mmh, it's not great to define Ractor because then things like this happen:
https://github.com/ruby/ruby-bench/actions/runs/19581337387/job/56079691198?pr=442

/home/runner/.rubies/truffleruby-25.0.0/lib/mri/psych.rb:709:in `config': undefined method `current' for class Ractor (NoMethodError)
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/psych.rb:725:in `load_tags='
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/psych.rb:741:in `<module:Psych>'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/psych.rb:234:in `<top (required)>'
	from <internal:core> core/kernel.rb:229:in `gem_original_require'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/bundled_gems.rb:69:in `require'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/yaml.rb:4:in `<top (required)>'
	from <internal:core> core/kernel.rb:229:in `gem_original_require'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/bundled_gems.rb:69:in `require'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/gems/gems/rubocop-1.79.1/lib/rubocop/config_loader_resolver.rb:4:in `<top (required)>'
	from <internal:core> core/kernel.rb:292:in `require_relative'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/gems/gems/rubocop-1.79.1/lib/rubocop.rb:778:in `<top (required)>'
	from <internal:core> core/kernel.rb:229:in `gem_original_require'
	from /home/runner/.rubies/truffleruby-25.0.0/lib/mri/bundled_gems.rb:69:in `require'
	from /home/runner/work/ruby-bench/ruby-bench/benchmarks/rubocop/benchmark.rb:11:in `<main>'

So I think we should either define Object#make_shareable (see #375 (comment)), or Object#deep_freeze.

[rafaelfranca]

I think since this is mostly for shim a method that doesn't exist anyway in some Ruby implementation Object#make_shareable should be fine

[eregon]

Done, and updated benchmarks to use Object#make_shareable. Should be good now (tried a few benchmarks locally) but I'll check CI.