fix(test): set ETL_DATA_ROOT to tmp_path in integration tests

save_metadata calls ensure_dataset_dirs which creates dirs under
ETL_DATA_ROOT (/app/data by default). In CI this path doesn't exist
and is not writable. Use monkeypatch to redirect to tmp_path.

Author: VTvito

tests/integration/test_service_endpoints.py

@@ -6,6 +6,7 @@
 import json
 import os
 import sys
+import tempfile
 
 import pytest
 from prometheus_client import REGISTRY
@@ -39,7 +40,11 @@ def _clear_app_modules():
 # ── Fixtures: Flask test clients ──
 
 @pytest.fixture
-def clean_nan_client():
+def clean_nan_client(tmp_path, monkeypatch):
+    monkeypatch.setenv("ETL_DATA_ROOT", str(tmp_path))
+    # Reload path_utils so it picks up the new ETL_DATA_ROOT
+    import common.path_utils as _pu
+    monkeypatch.setattr(_pu, "DATA_ROOT", str(tmp_path))
     _clear_app_modules()
     sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "services", "clean-nan-service"))
     from app import create_app