Issue: Incorrect `requires_grad` in the last diagram

[gggboy-9527]

In the tutorial Understanding requires_grad, retain_grad, Leaf, and Non-leaf Tensors, the last diagram (showing the computational graph) has an error.

It shows z = x @ W + b with requires_grad = False.
However, since W and b both have requires_grad = True, the output z should also have requires_grad = True.

Please correct the diagram to reflect this.

Thank you!