[hotfix] fix bug in sequence parallel test

[littsk]

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fixed #4888

📝 What does this PR do?

When enabling sequence parallelism during testing, the test fails. This pull request aims to address and rectify this issue.

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[github-actions]

The code coverage for the changed files is 66%.

Click me to view the complete report

Name                                          Stmts   Miss  Cover
-----------------------------------------------------------------
tests/test_shardformer/test_model/_utils.py     182     62    66%
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TOTAL                                           182     62    66%