make pad_to_sequence_len default to the same value as sample_packing (#2941) [skip ci]

* make pad_to_sequence_len default to the same value as sample_packing

* remove duplicate validation

* fix test

* update description meta

Co-authored-by: NanoCode012 <nano@axolotl.ai>

---------

Co-authored-by: NanoCode012 <nano@axolotl.ai>

tests/utils/schemas/validation/test_default_values.py

@@ -0,0 +1,21 @@
+"""Tests for default values for configurations"""
+
+from axolotl.utils.config import validate_config
+from axolotl.utils.dict import DictDefault
+
+
+class TestDefaultConfigValues:
+    """Tests for default values for configurations"""
+
+    def test_pad_to_sequence_len(self, min_base_cfg):
+        """Tests that sample packing automatically sets pad_to_sequence_len to True"""
+        cfg = (
+            DictDefault(
+                sample_packing=True,
+            )
+            | min_base_cfg
+        )
+
+        cfg = validate_config(cfg)
+
+        assert cfg.pad_to_sequence_len is True