[CI] Make MultiItemDataset a global variable after switch to spawn

tests/train/test_trainer_utils.py

@@ -840,22 +840,23 @@ def test_validate_generator_output_element_length_mismatch():
         validate_generator_output(len(input_batch["prompts"]), generator_output)
 
 
-def test_build_dataloader_seeding(dummy_config):
-    """Test that build_dataloader correctly seeds the dataloader for reproducible shuffling."""
+# Create a dataset with multiple distinct items to test shuffling
+class MultiItemDataset:
+    def __init__(self, size=10):
+        self.data = [f"item_{i}" for i in range(size)]
+
+    def __len__(self):
+        return len(self.data)
 
-    # Create a dataset with multiple distinct items to test shuffling
-    class MultiItemDataset:
-        def __init__(self, size=10):
-            self.data = [f"item_{i}" for i in range(size)]
+    def __getitem__(self, idx):
+        return self.data[idx]
 
-        def __len__(self):
-            return len(self.data)
+    def collate_fn(self, batch):
+        return batch
 
-        def __getitem__(self, idx):
-            return self.data[idx]
 
-        def collate_fn(self, batch):
-            return batch
+def test_build_dataloader_seeding(dummy_config):
+    """Test that build_dataloader correctly seeds the dataloader for reproducible shuffling."""
 
     dataset = MultiItemDataset(size=20)