Use larger atol in `torch.allclose` for some tests
# What does this PR do?

Running CI against torch 2.0 (and therefore CUDA 11.7), some tests for `BridgeTowerModel` failed:
- test_disk_offload
- test_cpu_offload
- test_model_parallelism

While with torch `1.13.1` (with CUDA 11.6), the difference between `base_output` and `new_output` in these 3 tests are 0.0, we get `1e-7 ~ 3e-6` as difference for torch `2.0`.

**Deep debugging reveals that the first non-zero difference occurs when `nn.MultiheadAttention` is called.**

This PR increase the atol to `1e-5` (the default one is `1e-8`) in `ModelTesterMixin`.

If we don't feel super good with this for all model tests, we can override these 3 tests in `BridgeTowerModelTest`.
(But when more models start using `nn.MultiheadAttention`, it's best to keep this larger value in common testing file)


_The documentation is not available anymore as the PR was closed or merged._