[skip ci] Update preview.yml

Fix warning message about snake case vs. kebab case for pypi publish action

Author: nnansters

.github/workflows/preview.yml

@@ -58,5 +58,5 @@ jobs:
         with:
           user: __token__
           password: ${{ secrets.TEST_PYPI_API_TOKEN}}
-          repository_url: https://test.pypi.org/legacy/
+          repository-url: https://test.pypi.org/legacy/
           skip-existing: true