Fix check on sdist version number

Package name is cupy_xarray, not cupy-xarray.

.github/workflows/pypi-release.yaml

@@ -45,7 +45,7 @@ jobs:
         run: |
           python -m twine check dist/*
           pwd
-          if [ -f dist/cupy-xarray-0.0.0.tar.gz ]; then
+          if [ -f dist/cupy_xarray-0.0.0.tar.gz ]; then
             echo "❌ INVALID VERSION NUMBER"
             exit 1
           else