[dynamo] Fix bug in tensor.item fake tensor propogation (#91668)
When we run the node with fake value for tensor.item, it would previously error because the utility method doesn't know how to handle placeholder node. The tensor we are calling item can be input from user will be placeholder in the graph.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91668
Approved by: https://github.com/voznesenskym
