Bump onnx from 1.13.0 to 1.15.0 in /requirements (#2986)

Bumps [onnx](https://github.com/onnx/onnx) from 1.13.0 to 1.15.0.
- [Release notes](https://github.com/onnx/onnx/releases)
- [Changelog](https://github.com/onnx/onnx/blob/main/docs/Changelog-ml.md)
- [Commits](onnx/onnx@v1.13.0...v1.15.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/dev.txt

@@ -6,7 +6,7 @@ pytest==7.4.*
 coverage==7.3.*
 pytest-timeout==2.2.*
 pytest-mock==3.12.*
-onnx==1.13.0
+onnx==1.15.0
 onnxruntime==1.14.1
 pytest-csv==3.0.*
 tox==4.11.*