test_setup: fix with newer setuptools

We are creating a fake dist here, and newer setuptools requires
some things to be explicitely set now, like where the packages live.

Author: lazka

tests/test_setup.py

@@ -36,6 +36,7 @@
 @fixture
 def dist(temp_po_dir) -> GDistribution:
     dist = GDistribution()
+    dist.packages = []
     dist.po_directory = str(temp_po_dir)
     return dist