increase sleep for TestCuda.test_caching_pinned_memory_multi_gpu (#76601)
Fixes #68299. Fixes #70875.
Test is flaky on ROCm because the HIP runtime occasionally copies asynchronously too quickly for the current sleep value of 50ms. This is not a bug. Increasing the sleep value to 1s to avoid flakiness.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76601
Approved by: https://github.com/pruthvistony, https://github.com/malfet
