OrasClient.push fails on Windows as empty Manifest Config uses /dev/null which is Linux specific

[sunnycarter]

My code runs fine on Linux. On Windows it fails with an error.

Here's my code:

        client = OrasClient(hostname=acr_url)
        
        client.login(
            username=self._manifest_credentials["username"],
            password=self._manifest_credentials["acr_token"],
        )
        target = (
                f"{client.remote.hostname.replace('https://', '')}/testartifact:1.0.0"
            )
        client.push(`
                files=["testartifact.json"],
                target=target
            )

 File "<>\oras\client.py", line 131, in push
    return self.remote.push(*args, **kwargs)
  File "<>\oras\provider.py", line 718, in push
    response = self.upload_blob(config_file, container, conf)
  File "<>\oras\provider.py", line 217, in upload_blob
    response = self.put_upload(blob, container, layer)
  File "<>\oras\provider.py", line 474, in put_upload
    with open(blob, "rb") as fd:
OSError: [Errno 22] Invalid argument: 'C:\\dev\\null'

I have made a fix for this and will submit a PR. The fix is in oci.py ManifestConfig:

        if platform.system() == "Windows":
            path = "nul"
        else:
            path = "/dev/null"

[sunnycarter]

#91 submitted to fix this

[sunnycarter]

Fixed in 0.1.18