Can't combine DatetimeIndex MultiIndex with numeric MultiIndex
- [ ] closes #23478
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry


@AlexGregory96 are there other concat tests in this file? I think https://github.com/pandas-dev/pandas/blob/b0082d2503a9c5b4732acfe09716f49670e0fe8f/pandas/tests/reshape/concat/test_index.py#L192 would be a more natural location This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. this needs a rebase This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. pls merge master and address comments thanks @Alex-Gregory-1 