Fix bitbucket wiki import with hashed storage enabled

What does this MR do?

Ensures the wiki is imported to disk_path rather than full_path, so importing in the hashed storage case works.

The project is imported using import_url so is unaffected by this bug.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Bug found in hashed storage audit

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #40292 (closed)