Upgrade from 10.0 to 11.4 migration fails

[rkemp435]

After upgrading from 10.0 to 11.4 the migration zerver.0742_usermessage_zerver_usermessage_is_private_unread_message_id repeatedly fails.

zulip-1 | django.db.utils.ProgrammingError: relation "zerver_usermessage_is_private_unread_message_id" already exists zulip-1 | zulip-1 | Applying zerver.0742_usermessage_zerver_usermessage_is_private_unread_message_id...Zulip migration failed with exit code 1. Exiting. zulip-1 exited with code 0

[rkemp435]

Fixing was as simple as dropping the index so the migration could recreate it, but it still seems like a bug that it was able to get itself in to this state.

[alexmv]

This was discussed in https://chat.zulip.org/#narrow/channel/31-production-help/topic/docker.2011.2E4.20migration.20fails/near/2336731. AFAIK the only way to get into this state would be to have the database server or Python upgrade process be interrupted or crash mid-migrations.