Fix conditional logic for setting pre and post hooks for batches

Previously we were doign an if+elif for setting pre and post hooks
for batches, where in the `if` matched if the batch wasn't the first
batch, and the `elif` matched if the batch wasn't the last batch. The
issue with this is that if the `if` was hit the `elif` _wouldn't_ be hit.
This caused the first batch to appropriately not run the `post-hook` but
then every hook after would run the `post-hook`.

core/dbt/task/run.py

@@ -813,8 +813,9 @@ def _submit_batch(
         # Only run pre_hook(s) for first batch
         if batch_idx != 0:
             node_copy.config.pre_hook = []
+
         # Only run post_hook(s) for last batch
-        elif batch_idx != len(batches) - 1:
+        if batch_idx != len(batches) - 1:
             node_copy.config.post_hook = []
 
         batch_runner = self.get_runner(node_copy)