fix unit test test_upgrade_schema

the test_migration.TestMigration.test_upgrade_schema unit test has been in the skipped state for many years. I tried running it and found some differences in the schemas:

https://www.diffchecker.com/hmdhK8tK/

(The diff contains a couple tables that as of writing this have not yet been implemented in the master branch: entity_class_display_mode and display_mode__entity_class)