Fix bitbucket server import interaction with :new_import_ui feature flag

What does this MR do?

See #227362 (closed) for details

Testing guidelines

1. You will need bitbucket server installation (quickest way is to run it with https://hub.docker.com/r/atlassian/bitbucket-server/, sorry atlassian trial license will be required)
2. Initiate import from bitbucket server
3. Import should be ok
4. Switch to :new_import_ui feature flag with rails console
5. Repeat steps 2-3

Demo

demo

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content