[AIRFLOW-XXX] Fix incorrect docstring parameter

[kaxil]

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Jira

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  old_state instead of old_states

Tests

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  Doc change

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Documentation

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[XD-DENG]

Hi @kaxil , seems there is the same error in line 758. Do you mind fixing it together?

[kaxil]

Done :)

[XD-DENG]

Have merged given I don't see any chance that it bringing in CI failure ;-)