Add a step in distribution test which checks if any of the artifacts exceeds 80 MB since Pypi has a per-file size limit.
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Closes#35831
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35831 from XuanWang-Amos:dist_test_add_size_check de50f20e14
PiperOrigin-RevId: 605664419