Add skips for lightgbm and treelite in tests

Author: lukehoffmann

improver_tests/calibration/rainforests_training/test_CompileRainForestsCalibration.py

@@ -11,6 +11,10 @@
     CompileRainForestsCalibration,
 )
 
+lightgbm = pytest.importorskip("lightgbm")
+tl2cgen = pytest.importorskip("tl2cgen")
+treelite = pytest.importorskip("treelite")
+
 
 def test__init__(lightgbm_available, treelite_available, tmp_path):
     """Test class is created if treelight libraries are available.

improver_tests/calibration/rainforests_training/test_TrainRainForestsCalibration.py

@@ -11,6 +11,8 @@
     TrainRainForestsCalibration,
 )
 
+lightgbm = pytest.importorskip("lightgbm")
+
 
 def test__init__lightgmb_available(lightgbm_available):
     """Test class is created if lightgbm library is available.