Set the ActiveRecord::Schema version when running the app:update task

[rafaelfranca]

See #44286 for the description of the problem.

This PR backport that feature and use the app:update task to make the upgrade easier.

Without it people would need to dump the database schema using Rails 7.0 before loading.

[kamipo]

Do we need to backport #44286 in 7-0-stable?

Actually the problem #43909 is due to #42297 changed the implicit default but didn't care the previous implicit default as precision: nil.

So I think just #44358 with re db:schema:dump is a reasonable solution to me.

[rafaelfranca]

We don't need to backport, but I prefer to do it. It is a small feature but make easier to people to upgrade. Asking people to run db:schema:dump while is equivalent to ask people to run app:update requires a database connection and it to already be with the correct schema loaded in Rails 6.1. That is more likely for people to mess up.

[matthewd]

Yeah, it otherwise technically requires a sequence of db:schema:load, [bump gemfile], app:update, db:schema:dump... which isn't terrible, but it just feels like avoidable complication. (Particularly, given how small this change is -- we're building on existing shipped migration-versioning support, so risk/reward seems worthwhile.)