Mamba / FalconMamba: Fix mamba left padding (#32677)

* fix mamba left padding

* Apply suggestions from code review

Co-authored-by: Pablo Montalvo <39954772+molbap@users.noreply.github.com>

* fix copies

* test with `inputs_embeds`

* Update src/transformers/models/falcon_mamba/modeling_falcon_mamba.py

Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

* copies

* clairfy

* fix last comments

* remove

---------

Co-authored-by: Pablo Montalvo <39954772+molbap@users.noreply.github.com>
Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

tests/models/mamba/test_modeling_mamba.py

@@ -94,6 +94,7 @@ class MambaModelTester:
         self, gradient_checkpointing=False, scale_attn_by_inverse_layer_idx=False, reorder_and_upcast_attn=False
     ):
         input_ids = ids_tensor([self.batch_size, self.seq_length], self.vocab_size)
+        attention_mask = ids_tensor([self.batch_size, self.seq_length], 1)
 
         sequence_labels = None
         token_labels = None
@@ -112,7 +113,7 @@ class MambaModelTester:
         return (
             config,
             input_ids,
-            None,
+            attention_mask,
             sequence_labels,
             token_labels,
             choice_labels,
@@ -146,6 +147,7 @@ class MambaModelTester:
         (
             config,
             input_ids,
+            attention_mask,
             sequence_labels,
             token_labels,
             choice_labels,
@@ -154,6 +156,7 @@ class MambaModelTester:
         return (
             config,
             input_ids,
+            attention_mask,
             sequence_labels,
             token_labels,
             choice_labels,
@@ -246,12 +249,12 @@ class MambaModelTester:
         (
             config,
             input_ids,
-            _,
+            attention_mask,
             sequence_labels,
             token_labels,
             choice_labels,
         ) = self.prepare_config_and_inputs()
-        inputs_dict = {"input_ids": input_ids}
+        inputs_dict = {"input_ids": input_ids, "attention_mask": attention_mask}
         return config, inputs_dict