Added support for Ruby < 3.0.x in IRB.BypassReloader

Me again :)

I was trying to use irb-config with a Rails 3.0.x app that cannot be upgraded right away to 3.2.x, and found that it wouldn't work due to ActionDispatch::Reloader not being defined in such scenario.

So here is a little patch that uses ActionDispatch::Callbacks instead for earlier versions of Rails. This way pry starts without complaining.

Cheers
Vito