fix incorrect step access method in documentation (#3483)

Author: marwan37

docs/book/component-guide/experiment-trackers/comet.md

@@ -142,7 +142,7 @@ You can find the URL of the Comet experiment linked to a specific ZenML run via
 from zenml.client import Client
 
 last_run = client.get_pipeline("<PIPELINE_NAME>").last_run
-trainer_step = last_run.get_step("<STEP_NAME>")
+trainer_step = last_run.steps["<STEP_NAME>"]
 tracking_url = trainer_step.run_metadata["experiment_tracker_url"].value
 print(tracking_url)
 ```

docs/book/component-guide/experiment-trackers/mlflow.md

@@ -168,7 +168,7 @@ You can find the URL of the MLflow experiment linked to a specific ZenML run via
 from zenml.client import Client
 
 last_run = client.get_pipeline("<PIPELINE_NAME>").last_run
-trainer_step = last_run.get_step("<STEP_NAME>")
+trainer_step = last_run.steps["<STEP_NAME>"]
 tracking_url = trainer_step.run_metadata["experiment_tracker_url"].value
 print(tracking_url)
 ```

docs/book/component-guide/experiment-trackers/wandb.md

@@ -152,7 +152,7 @@ You can find the URL of the Weights & Biases experiment linked to a specific Zen
 from zenml.client import Client
 
 last_run = client.get_pipeline("<PIPELINE_NAME>").last_run
-trainer_step = last_run.get_step("<STEP_NAME>")
+trainer_step = last_run.steps["<STEP_NAME>"]
 tracking_url = trainer_step.run_metadata["experiment_tracker_url"].value
 print(tracking_url)
 ```

docs/book/how-to/popular-integrations/mlflow.md

@@ -71,7 +71,7 @@ You can find the URL to the MLflow experiment for a ZenML run:
 
 ```python
 last_run = client.get_pipeline("<PIPELINE_NAME>").last_run
-trainer_step = last_run.get_step("<STEP_NAME>")
+trainer_step = last_run.steps["<STEP_NAME>"]
 tracking_url = trainer_step.run_metadata["experiment_tracker_url"].value
 ```