Update testenvs with minimal app config

Worked out by Beth Probert

tests/unit_tests/test_metadata.py

@@ -1,6 +1,7 @@
 """Tests that captures have the expected metadata."""
 
 import json
+import tempfile
 from datetime import datetime
 from pathlib import Path
 
@@ -99,7 +100,8 @@ def test_env() -> LabThingsTestEnv:
         "stage": DummyStage,
         "bg_channel_deviations_luv": ChannelDeviationLUV,
     }
-    with LabThingsTestEnv(things=thing_conf) as env:
+    app_config = {"data_folder": tempfile.gettempdir()}
+    with LabThingsTestEnv(things=thing_conf, application_config=app_config) as env:
         yield env