Fix tests that fail when run outside Docker (#122)

## Changes
- Include db_client fixture which sets DB-related environment variables
  that aren't set by default when running outside the container

## Context
Outside the container the environment variables from local.env aren't
automatically set which caused some db tests to fail. This PR includes
the db_client fixture that sets those environment variables.

app/tests/conftest.py

@@ -11,10 +11,17 @@
 import api.logging
 import tests.api.db.models.factories as factories
 from api.db import models
+from api.util.local import load_local_env_vars
 from tests.lib import db_testing
 
 logger = logging.getLogger(__name__)
 
+
+@pytest.fixture(autouse=True)
+def env_vars():
+    load_local_env_vars()
+
+
 ####################
 # Test DB session
 ####################