Fix TestPyPI publish: skip-existing for duplicate version uploads

Version 0.0.1 already exists on TestPyPI from the initial push.
Subsequent pushes to main that touch sdk/python/ trigger the
publish workflow, which fails with 400 Bad Request because you
can't re-upload the same version. skip-existing: true handles
this gracefully.

Author: Jovonni

.github/workflows/publish-sdk.yml

@@ -54,6 +54,7 @@ jobs:
         uses: pypa/gh-action-pypi-publish@release/v1
         with:
           repository-url: https://test.pypi.org/legacy/
+          skip-existing: true
 
   publish-pypi:
     name: Publish to PyPI