Update Dockerfile to use python 3.12

[lixinso]

python 3.9 does not compatible with latest Semantic Kernel

Description

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• [ ] The pull request does not introduce [breaking changes].
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Testing Guidelines

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[github-actions[bot]]

Hi, thank you for your interest in helping to improve the prompt flow experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment.

[lixinso]

Linking to the issues, https://github.com/microsoft/promptflow/issues/3830

[github-actions[bot]]

Hi, thank you for your interest in helping to improve the prompt flow experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment.