Fix PyPI publish action for uppercase repo names

Disable attestations to avoid Docker image reference error caused by
uppercase letters in repository name (CoplayDev/unity-mcp). Docker
requires lowercase image references.

The trusted publishing (OIDC) already provides supply chain security.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/actions/publish-pypi/action.yml

@@ -19,3 +19,4 @@ runs:
       uses: pypa/gh-action-pypi-publish@release/v1
       with:
         packages-dir: Server/dist/
+        attestations: false