Only import matplotlib where necessary for artifact plotting (mlflow#3703)

* Only import matplotlib where necessary for artifact plotting

Signed-off-by: Corey Zumar <corey.zumar@databricks.com>

* Silly change for formatter

Signed-off-by: Corey Zumar <corey.zumar@databricks.com>
Signed-off-by: harupy <17039389+harupy@users.noreply.github.com>

Author: harupy

mlflow/sklearn/utils.py

@@ -4,7 +4,6 @@
 import inspect
 import logging
 from numbers import Number
-import matplotlib.pyplot as plt
 import numpy as np
 import time
 
@@ -500,6 +499,8 @@ def _log_specialized_estimator_content(fitted_estimator, run_id, fit_args, fit_k
                     display.ax_.set_title(artifact.title)
                     filepath = tmp_dir.path("{}.png".format(artifact.name))
                     display.figure_.savefig(filepath)
+                    import matplotlib.pyplot as plt
+
                     plt.close(display.figure_)
                 except Exception as e:  # pylint: disable=broad-except
                     _log_warning_for_artifacts(artifact.name, artifact.function, e)