[Build] no source distribution in PyPI

### Describe the issue

I'd like to use onnxruntime against alternative Python implementations (e.g. Pyston, which is API-compatible with CPython, but not ABI-compatible), but the source is not included in PyPI. So pip is not able to build the package using the standard Python workflow.

https://pypi.org/project/onnxruntime/#files

### Urgency

My application has several dependencies with C extensions. onnxruntime is the only dependency that does not publish the source distribution to PyPI, and presenting this problem. We're blocked from migrating to Pyston (which is 20% faster for our app), without having to do some non-standard workflow for building onnxruntime (i.e. not via pip).

### Target platform

x86_64

### Build script

```
pyston3.8 -m pip install onnxrunitme
```

### Error / output

```
ERROR: Could not find a version that satisfies the requirement onnxruntime (from versions: none)
ERROR: No matching distribution found for onnxruntime
```

### Visual Studio Version

_No response_

### GCC / Compiler Version

_No response_

Start by reviewing the repository's Python packaging and release workflow, then compare the artifacts currently listed on the linked PyPI project page with the source-distribution requirement. Verify that pip can build and install the package from the published source distribution on an alternative Python implementation such as Pyston.

Written by the indexing model from the issue text.