fix longformer slow down (#5811)

Author: patrickvonplaten

src/transformers/modeling_longformer.py

@@ -311,7 +311,7 @@ def forward(
         # is index masked or global attention
         is_index_masked = attention_mask < 0
         is_index_global_attn = attention_mask > 0
-        is_global_attn = any(is_index_global_attn.flatten())
+        is_global_attn = is_index_global_attn.flatten().any().item()
 
         hidden_states = hidden_states.transpose(0, 1)