This PR deprecates the use of the name "primary" as the connection_specification_name for ActiveRecord::Base in favor of using "ActiveRecord::Base" to avoid confusion as earlier the classname was used in any other case.
The usage of the Range#include? method to check the inclusion of an argument in date-time with zone range is deprecated in Ruby and since Rails extends it, the deprecation needs to be carried forward. As a replacement, it is recommended to use Range#cover?
Before this bugfix, if an app called establish_connection with no arguments or doesn't call connects_to in ApplicationRecord and uses parallel testing databases, the application could've picked up the wrong configuration.
