chore: fix typing for manifest_config param of push fn

[tarilabs]

for push() the parameter manifest_config seems to me has the wrong type annotation.

oras-py/oras/provider.py

Line 681 in 9527aa1

manifest_config: Optional[dict] = None,

while it should be an Optional[str]

considering it's used in push() to be passed to _parse_manifest_ref()

oras-py/oras/provider.py

Lines 785 to 786 in 9527aa1

	if manifest_config:
	ref, media_type = self._parse_manifest_ref(manifest_config)

which expect a str (and not a dict)

oras-py/oras/provider.py

Lines 228 to 246 in 9527aa1

	def _parse_manifest_ref(self, ref: str) -> Tuple[str, str]:
	"""
	Parse an optional manifest config.
	Examples
	--------
	<path>:<content-type>
	path/to/config:application/vnd.oci.image.config.v1+json
	/dev/null:application/vnd.oci.image.config.v1+json
	:param ref: the manifest reference to parse (examples above)
	:type ref: str
	:return - A Tuple of the path and the content-type, using the default unknown
	config media type if none found in the reference
	"""
	path_content: PathAndOptionalContent = oras.utils.split_path_and_content(ref)
	if not path_content.content:
	path_content.content = oras.defaults.unknown_config_media_type
	return path_content.path, path_content.content

hope this helps :)