Don't have public attributes marked as private

tests/rpc/test_rpc_apiserver.py

@@ -1734,7 +1734,7 @@ def test_api_backtesting(botclient, mocker, fee, caplog, tmpdir):
     assert result['status_msg'] == 'Backtest ended'
 
     # Simulate running backtest
-    ApiBG._bgtask_running = True
+    ApiBG.bgtask_running = True
     rc = client_get(client, f"{BASE_URI}/backtest/abort")
     assert_response(rc)
     result = rc.json()
@@ -1763,7 +1763,7 @@ def test_api_backtesting(botclient, mocker, fee, caplog, tmpdir):
     result = rc.json()
     assert 'Bot Background task already running' in result['error']
 
-    ApiBG._bgtask_running = False
+    ApiBG.bgtask_running = False
 
     # Rerun backtest (should get previous result)
     rc = client_post(client, f"{BASE_URI}/backtest", data=data)