Error when logging to MLFlow deleted experiment (#20556)

* Make error MLFlow deleted experiment explicit

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
(cherry picked from commit 29ed24f)

Author: 2 people

src/lightning/pytorch/loggers/mlflow.py

@@ -180,7 +180,7 @@ def experiment(self) -> "MlflowClient":
 
         if self._experiment_id is None:
             expt = self._mlflow_client.get_experiment_by_name(self._experiment_name)
-            if expt is not None:
+            if expt is not None and expt.lifecycle_stage != "deleted":
                 self._experiment_id = expt.experiment_id
             else:
                 log.warning(f"Experiment with name {self._experiment_name} not found. Creating it.")