fix tf led pt test (#9513)

tests/test_modeling_tf_led.py

@@ -166,7 +166,13 @@ def prepare_led_inputs_dict(
     if attention_mask is None:
         attention_mask = tf.cast(tf.math.not_equal(input_ids, config.pad_token_id), tf.int8)
     if decoder_attention_mask is None:
-        decoder_attention_mask = tf.cast(tf.math.not_equal(decoder_input_ids, config.pad_token_id), tf.int8)
+        decoder_attention_mask = tf.concat(
+            [
+                tf.ones(decoder_input_ids[:, :1].shape, dtype=tf.int8),
+                tf.cast(tf.math.not_equal(decoder_input_ids[:, 1:], config.pad_token_id), tf.int8),
+            ],
+            axis=-1,
+        )
     return {
         "input_ids": input_ids,
         "attention_mask": attention_mask,