Latest protobuf version not compatible with current onnx version

[jacobolofsson]

finn-base[onnx] is pinned to use onnx==1.7.0, which is not compatible with protobuf>3.20. This is solved in onnx==1.12 by introducing an upper constraint on the protobuf version (onnx/onnx#4222)

Possible solutions would be:

1. Upgrade onnx to >= 1.12
2. Add protobuf<3.21 as a direct dependency

I would be happy to create a PR to implement either of these

[maltanar]

Hi Jacob, thanks for pointing this out. This repo (finn-base) is scheduled to be deprecated soon, and should be replaced in any dependent projects with the new QONNX (https://github.com/fastmachinelearning/qonnx) repo. QONNX is nearly a drop-in replacement for finn-base, only a namespace change is needed (e.g. import finn.core.modelwrapper becomes import qonnx.core.modelwrapper).