Fix disabling strict_loading when enabled by default

[lucthev]

Summary

When strict_loading is enabled by default, trying to explicitly disable strict loading at the relation level doesn't work:

class Developer < ApplicationRecord
  self.strict_loading_by_default = true
end

developer = Developer.strict_loading(false).first
developer.strict_loading? # => true

This PR ensures that .strict_loading(false) results in records which don't strictly load, even when enabled by default.

Other Information

Use-case: in an app with strict loading globally enabled (config.active_record.strict_loading_by_default = true), there's some contexts (noodling around in a Rails console, say) where you want a quick escape hatch.

[eileencodes]

Thanks! Congrats on your first PR to Rails 🎉

I've backported this to 7-0-stable in f99f422