Conflict when merging evidences

[marcorusc]

Describe the bug
Hello! As always, great job with pypath!

As discussed previously with @deeenes , I am getting an error when I load an existing interaction from two different sources in the same network object.

To Reproduce
Steps to reproduce the behavior:

1. Create an empty Network object
2. Add an interaction from any database
3. Add again the same interaction into the network (fastest way to reproduce the bug, it happen even if the interactions comes from different sources)
   

Expected behavior
The interaction is added to the network and the references and evidences are correctly merged (I suppose...).

Desktop (please complete the following information):

• OS: [Ubuntu 22.10]
• Python version: [3.10]
• Version or commit hash [v 0.15.4]