Fix mypy check failure and val_check_interval initialization in case of time based validation.

Author: Sohaib-Ahmed21

src/lightning/pytorch/trainer/setup.py

@@ -90,8 +90,6 @@ def _init_debugging_flags(
         trainer._val_check_time_interval = None  # default
         if isinstance(val_check_interval, (str, dict, timedelta)):
             trainer._val_check_time_interval = _parse_time_interval_seconds(val_check_interval)
-            # Keep the numeric scheduler neutral; loops should check the time-based attribute.
-            trainer.val_check_interval = 1.0
         else:
             trainer.val_check_interval = _determine_batch_limits(val_check_interval, "val_check_interval")
 

src/lightning/pytorch/trainer/trainer.py

@@ -498,7 +498,7 @@ def __init__(
         self._logger_connector.on_trainer_init(logger, log_every_n_steps)
 
         # init debugging flags
-        self.val_check_batch: Union[int, float]
+        self.val_check_batch: Optional[Union[int, float]] = None
         self.val_check_interval: Union[int, float]
         self.num_sanity_val_steps: Union[int, float]
         self.limit_train_batches: Union[int, float]