pin `apex` to a speicifc commit (for DeepSpeed CI docker image)
# What does this PR do?

The docker image build for DeepSpeed job in CI fails since ~ one week due to this [apex issue](https://github.com/NVIDIA/apex/issues/1679).

Let's pin to the previous commit until the above mentioned issue is resolved on `apex` side.

Currently, the DeepSpeed job fails as the above failure prevents to use newer images that include some fixes on  `accelerate` side.
_The documentation is not available anymore as the PR was closed or merged._