Install `sentencepiece` in `DeepSpeed` CI image
# What does this PR do?

Install `sentencepiece` in `DeepSpeed` CI image. 
  - The new base image has no `sentencepiece` pre-installed, but it's required for DeepSpeed CI tests
  - With this PR, the tests all pass (on single GPU runner)
_The documentation is not available anymore as the PR was closed or merged._<|||||>It's done :-) as suggested