[Fix] make all tests pass on XPU

[faaany]

What does this PR do?

When running make test on XPUs, I got the following test results:

FAILED tests/test_kwargs_handlers.py::KwargsHandlerTester::test_grad_scaler_kwargs - AttributeError: 'GradScaler' object has no attribute '_init_scale'
FAILED tests/test_optimizer.py::OptimizerTester::test_accelerated_optimizer_step_was_skipped - AssertionError: False is not true

The failed reason for these 2 tests is the same: XPU hasn't implemented torch.xpu.amp.GradScaler yet and in the current logic, self.scaler will be set to torch.cuda.amp.GradScaler as shown here.
To make the tests pass on XPU devices, we should skip these 2 tests on XPUs.

In addition to that, I noticed that there is no require_npu function in the testing.py. So I added it to the patch.

I am not sure whether it would be better to just use require_cuda instead of the combi of require_non_cpu and require_non_xpu. My goal is just to make all these tests work on XPU. Please let me know your thoughts. And if this patch is too small, just let me know as well. I can think about more tests related to XPU. Thanks a lot!

@muellerzr

[HuggingFaceDocBuilderDev]

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[muellerzr]

Thanks, this skip format is indeed the right way!