added support for exporting of t5 to onnx with past_key_values (#10651)

src/transformers/models/t5/modeling_t5.py

@@ -423,6 +423,8 @@ class T5Attention(nn.Module):
         # past_key_value[0] is (batch_size, n_heads, q_len - 1, dim_per_head)
         batch_size, seq_length = hidden_states.shape[:2]
 
+        int_seq_length = int(seq_length)
+        
         real_seq_length = seq_length
 
         if past_key_value is not None:
@@ -489,7 +491,7 @@ class T5Attention(nn.Module):
             # if key and values are already calculated
             # we want only the last query position bias
             if past_key_value is not None:
-                position_bias = position_bias[:, :, -seq_length:, :]
+                position_bias = position_bias[:, :, -int_seq_length:, :]
 
             if mask is not None:
                 position_bias = position_bias + mask  # (batch_size, n_heads, seq_length, key_length)