fix: set returncode=0 in cli integration test mock

The mock was missing an explicit returncode, so it defaulted to a
MagicMock object which != 0, causing the failure path to be taken.

Author: b-per

tests/unit/dbt_cli/test_cli_integration.py

@@ -15,6 +15,7 @@ def test_dbt_command_execution(self, mock_popen):
         """
         # Mock setup
         mock_process = MagicMock()
+        mock_process.returncode = 0
         mock_process.communicate.return_value = ("command output", None)
         mock_popen.return_value = mock_process