Fix wrapper access in the scheduler

[bryanp]

Description

I've noticed this error lately in my recent use of async-io:

/Users/bryanp/.gem/ruby/3.0.0/gems/async-1.28.9/lib/async/scheduler.rb:74:in `ensure in io_wait': undefined method `reactor=' for nil:NilClass (NoMethodError)
	from /Users/bryanp/.gem/ruby/3.0.0/gems/async-1.28.9/lib/async/scheduler.rb:74:in `io_wait'
	from /Users/bryanp/.rubies/ruby-3.0.0/lib/ruby/3.0.0/socket.rb:304:in `__sendmsg'
	from /Users/bryanp/.rubies/ruby-3.0.0/lib/ruby/3.0.0/socket.rb:304:in `sendmsg'

It's been quite tough to reproduce on demand but happens enough I thought it warranted bringing up for discussion.

Types of Changes

• Bug fix.

Testing

• I tested my changes locally.

[ioquatix]

We have completely removed the need for this in the current implementation. For the current stable-v1 branch, this may still be applicable.

[ioquatix]

Thanks for your contribution.