Resets the ActiveRecord::Base connection after rails db:migrate:name

[kylekthompson]

Summary

While working on #38586, I noticed that there was a slight additional inconsistency in the rails db:migrate:name commands. While rails db:migrate was resetting the ActiveRecord::Base connection back to the original configuration, rails db:migrate:name was not.

With these changes, the behaviors will line up going forward.

[eileencodes]

Thanks!