we need to register test backend first before using test device of third-party accelerators
Author: ji-huazhong
Pull request: yes

# What does this PR do?

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Fixes  https://github.com/huggingface/transformers/pull/25870#issuecomment-1754523487


## Before submitting
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cc @ydshieh 


Comments:
https://github.com/huggingface/transformers/pull/25870 contains the modifications of this PR, closed