Fix regression with old wiki image uploads

What does this MR do?

In !48763 (merged), we introduced a regression that makes old wiki uploads links unavailable because the project namespace was not set. This means that, for example, all images in the wiki will 404.

Images were added as regular uploads until 11.3, so a lot of wikis can be affected.

Refs #300120 (closed)

Screenshots

Before the fix

After the fix

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content