I am not sure whether going down this path is the best approach. I feel
that perhaps ActiveSupport could require everything within
active_support/core_ext to ensure that active_support/core_ext can load
itself. Still, there's no changing old versions of Rails, so I suppose
this solution works? I am also not sure what the Rails team would
recommend when it comes to requiring specific pieces of ActiveSupport
(to leverage things like mattr_accessor).

In any case, I was able to reproduce the CI failures locally and these
changes make everything pass for me locally.