Fix forward-mode AD formula for binary_cross_entropy_with_logits
The problem was that `grad_input` and `grad_target` may be ZeroTensors,
which are immutable. This PR changes it so that operations on grad_input
and grad_target in `binary_cross_entropy_with_logits_jvp` are no longer
in-place.
Test Plan:
- run existing tests
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76322
Approved by: https://github.com/soulitzer
