Proc's self should be shareable.

[ko1]

To fix the issue https://bugs.ruby-lang.org/issues/18243
we need to make sure the Proc's self is shareable.
These procs are used by define_method and it doesn't use
Proc's self, so nil is enough.

[marcandre]

Thanks for the PR. Would the current test suite of ostruct fail once ruby/ruby#5232 is merged?

[ko1]

ruby/ruby#5232 contains same patch for ruby/ruby (to prevent the failure).

So the answer is:

• YES, this patch is needed.
• No, this patch is contained in the ruby/ruby's PR.

[ko1]

if this PR is merged quickly and apply to ruby/ruby, I'll rebase ruby/ruby#5232 on it.

[marcandre]

Done, and pushed to main repo too as 9c26931635

[ko1]

Thank you!!