fix: filter bug for keywork cause code can not reach

[yihong0618]

Summary

found by type checking for the filter is a keyword for python default the code below can no reach.
This patch fix it by correct to filters

if not isinstance(filter, list):

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Checklist

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• This change requires a documentation update, included: Dify Document
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• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
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