(py-)onnx: add v1.16.1

[wdconinc]

This PR adds onnx and py-onnx 1.16.1. This is a bugfix releases, onnx/onnx@v1.16.0...v1.16.1, onnx/onnx#6108.

Of potential interest, this version fixes running after gcc-8, but we haven't been keeping compiler conflicts in this package so I didn't add it to 1.16.0.

[spackbot-app]

Hi @wdconinc! I noticed that the following package(s) don't yet have maintainers:

• onnx
• py-onnx

Are you interested in adopting any of these package(s)? If so, simply add the following to the package class:

    maintainers("wdconinc")

If not, could you contact the developers of this package and see if they are interested? You can quickly see who has worked on a package with spack blame:

$ spack blame onnx

Thank you for your help! Please don't add maintainers without their consent.

You don't have to be a Spack expert or package developer in order to be a "maintainer," it just gives us a list of users willing to review PRs or debug issues relating to this package. A package can have multiple maintainers; just add a list of GitHub handles of anyone who wants to volunteer.