[pitivi] tests: Fix unit test setup method

[Alexandru Băluț <alexbalut src gnome org>]

commit f7bf2ccef4bf37c440e0756941dcba055937a5a6
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Tue May 31 14:20:28 2022 +0200

    tests: Fix unit test setup method
    
    When specifying two clips backed by the same asset, the asset should be
    added to the project only once.

 tests/common.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/tests/common.py b/tests/common.py
index 2d1a0268f..3f895999a 100644
--- a/tests/common.py
+++ b/tests/common.py
@@ -268,7 +268,7 @@ def setup_project_with_clips(assets_names: List[str]):
     def decorator(func):
         nonlocal assets_names
 
-        @setup_project(assets_names)
+        @setup_project(list(set(assets_names)))
         def wrapper(self):
             assets = self.app.project_manager.current_project.list_assets(GES.UriClip)