re-add testpypi publish step (open-telemetry#2991)

Author: lzchen

.github/workflows/release.yml

@@ -81,14 +81,13 @@ jobs:
       # rejected by pypi (e.g "3 - Beta"). This would cause a failure during the
       # middle of the package upload causing the action to fail, and certain packages
       # might have already been updated, this would be bad.
-      # EDIT: 5/31/2024 - TestPypi now requires a verified email. Commenting out as a temporary measure
-      # until we found TestPypi credentials.
-      # - name: Publish to TestPyPI
-      #   env:
-      #     TWINE_USERNAME: '__token__'
-      #     TWINE_PASSWORD: ${{ secrets.test_pypi_token }}
-      #   run: |
-      #     twine upload --repository testpypi --skip-existing --verbose dist/*
+
+      - name: Publish to TestPyPI
+        env:
+          TWINE_USERNAME: '__token__'
+          TWINE_PASSWORD: ${{ secrets.test_pypi_token }}
+        run: |
+          twine upload --repository testpypi --skip-existing --verbose dist/*
 
       - name: Publish to PyPI
         env: