update protobuf dependency to v5.x in accordance with most recent protoletariat version

[nielspardon]

It seems the protobuf dependency version was fixed to 3.20.11 but the version of protoletariat wasn't fixed.

substrait-python/pyproject.toml

Line 16 in a631919

gen_proto = ["protobuf == 3.20.1", "protoletariat >= 2.0.0"]

This leads to us pulling in the latest protoletariat version which has been updated to use protobuf v5.29.4 in March 2025.
https://github.com/cpcloud/protoletariat/releases/tag/3.3.10

I guess we want to keep the protobuf version in sync with the protoletariat dependency.