[nn/parallel/data_parallel.py]: Rename "_pre_bacward" method of ZeroDDP to "_pre_backward"

[junxu]

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📝 What does this PR do?

Rename "_pre_bacward" method of ZeroDDP to "_pre_backward".

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[FrankLeeeee]

LGTM. Will merge when checks are passed.

[FrankLeeeee]

Hi, seems some Github updates broke our CI checks. I have fixed the CI and can you rebase your code with the latest code so that the correct CI can be triggered?

[github-actions[bot]]

The code coverage for the changed files is 78%.

Click me to view the complete report

Name                                      Stmts   Miss  Cover
-------------------------------------------------------------
colossalai/nn/parallel/data_parallel.py     386     85    78%
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TOTAL                                       386     85    78%