Hi guys,
Thanks for your help, I have found the issue.
If that can help someone here is how :
It was indeed located inside the database, in the wordpress "options" table. It was the value of one of the element from divi builder. I don't know how it was injected there but I have removed it.
In order to locate it, I downloaded the whole database as SQL file and I used a code editor to bulk search some special terms in the whole database (like "atob" or "blob").
Have a good day !
Best.