In Rails engine, migration files are in under `db/migrate` of engine.
Therefore, when rake task is executed in engine, `db/migrate` is
automatically added to `DatabaseTasks.migrations_paths`.
https://github.com/rails/rails/blob/a18cf23a9cbcbeed61e8049442640c7153e0a8fb/activerecord/lib/active_record/railtie.rb#L39..L43

However, if execute the rake task under dummy app, migration files will not
be loaded because engine's migration path setting process is not called.

Therefore, in order to load migration files correctly, it is necessary to
execute rake task under engine.

Fixes #30765