Bump onnx from 1.8.1 to 1.10.1 in /ngraph/python

Bumps [onnx](https://github.com/onnx/onnx) from 1.8.1 to 1.10.1.
- [Release notes](https://github.com/onnx/onnx/releases)
- [Changelog](https://github.com/onnx/onnx/blob/master/docs/Changelog.md)
- [Commits](onnx/onnx@v1.8.1...v1.10.1)

---
updated-dependencies:
- dependency-name: onnx
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

ngraph/python/requirements_test.txt

@@ -2,7 +2,7 @@ flake8==3.9.0
 flake8-comprehensions==3.3.0
 flake8-docstrings==1.6.0
 flake8-quotes==3.2.0
-onnx==1.8.1
+onnx==1.10.1
 pydocstyle==5.1.1
 pytest==6.1.2
 retrying==1.3.3