Support kquant mixed for whisper export (#28515)
### Description
As titled.
### Motivation and Context
whisper-small in int4-kquant-mixed is close to int8.
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
