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`.
a18cf23a9c/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
Currently, all rails commands can be executed in engine,
but `server`, `console`, `dbconsole` and `runner` do not work.
This make all rails commands work in engine.
Related to #22588
