[CI] fix horovod tests

[otaj]

What does this PR do?

Horovod tests are failing with mysterious errors

Does your PR introduce any breaking changes? If yes, please list them.

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cc @tchaton @rohitgr7 @carmocca @akihironitta @Borda @awaelchli @justusschock @kaushikb11

[otaj]

For completeness sake of what broke - Horovod tests were broken due to NCCL, which from 2.12.7 broke when linked against dynamic libcudart - NVIDIA/nccl#658

The solution is to forcefully downgrade to the last working version 2.11.4, which will then be picked up by Horovod when compiling.

Added couple small improvements to how GPU tests are being run (and the environment being prepared)

[otaj]

This will be ready to merge once Docker images are built and pushed to dockerhub

[awaelchli]

🎉

[Borda]

Are we aware that the GPU tests are skipped?
https://dev.azure.com/Lightning-AI/lightning/_build/results?buildId=92435&view=logs&jobId=3f274fac-2e11-54ca-487e-194c91f3ae9f