Fixed a couple of mistakes in type annotations in optim package (#90216)
Doing some tests with all Optimizer and LRScheduler classes in optim package, I noticed a couple of mistakes in type annotations, so created a pull request to fix them.
- In Optimizer class, incorrectly named parameter `default` instead of `defaults` in pyi file
- In SGD class, type for `maximize` and `differentiable` not available in either py or pyi files
I don't know if there is a plan to move all types from pyi to py files, so wasn't too sure where to fix what.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90216
Approved by: https://github.com/janeyx99
