When importing a Zephyr Test, sometimes the attachments are not migrated

Zephyr attachments may be stored under any of the previous keys of a given project (including the current one). As of Xray 3.3.0, we are just looking for the attachments in the current directory.

Steps to reproduce:
1) Create a new project (key: AAA)
2) Create a Zephyr Test with a single step and an attachment
3) Change the project key to BBB
4) Create a Zephyr Test with a single step and an attachment
5) Change the project key to CCC
6) Create a Zephyr Test with a single step and an attachment
7) Import the project, some of the attachments will not be migrated