Add beam_PostCommit_Python_ValidatesDistrolessContainer_Dataflow

[damondouglas]

This PR closes #33003, adding scheduled checks for Python SDK (non ML) distroless variants via GitHub workflows.

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[damondouglas]

I want to wait at least 24 hours from when fc9083b35f982d3f1c5579cc0d06e9ae87689f77 merged before flipping this PR to ready.

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