fix(authenticated_http/storage_push_file): fix and add type annotation

src/aleph/sdk/client/authenticated_http.py

@@ -131,7 +131,7 @@ async def ipfs_push_file(self, file_content: bytes) -> str:
  resp.raise_for_status()
  return (await resp.json()).get("hash")
 
- async def storage_push_file(self, file_content) -> str:
+ async def storage_push_file(self, file_content: bytes) -> Optional[str]:
  """
  Push a file to the storage service.
  """