dataframe sparse to_coo test GH#25270

- [ ] closes #25270 (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

I think the new test cases and the test case above are duplicated test cases. We can merge the two cases into one. Or close this PR and the GH since it is already tested somewhat. Thanks for the investigation @liang3zy22 but you're correct; it looks like this has already been tested so let's close to avoid duplication