docs: fix log_metrics step description (#21109)

docs: fix log_metrics step description (#20677)

Co-authored-by: Alexander Zhipa <[email protected]>

Author: clumsy

src/lightning/pytorch/trainer/connectors/logger_connector/logger_connector.py

@@ -93,8 +93,9 @@ def log_metrics(self, metrics: _OUT_DICT, step: Optional[int] = None) -> None:
 
         Args:
             metrics: Metric values
-            step: Step for which metrics should be logged. Default value is `self.global_step` during training or
-                the total validation / test log step count during validation and testing.
+            step: Step for which metrics should be logged. If a `step` metric is logged, this value will
+                be used else will default to `self.global_step` during training or the total log step count
+                during validation and testing.
 
         """
         if not self.trainer.loggers or not metrics: