id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
1319724885,I_kwDOAMm_X85OqWdV,6838,sel by slice not working for multi-index containing float-values,57088171,open,0,4160723,,3,2022-07-27T15:22:07Z,2022-09-27T10:37:44Z,,NONE,,,,"### What happened?

```python
da = xr.DataArray(np.random.rand(4), {'x': np.arange(4)})
da = da.assign_coords(y=('x', np.linspace(0, 1, 4)))
da = da.assign_coords(z=('x', np.arange(4) + 4))
da.set_index(x=[""y"", ""z""]).sel(y=slice(None, 0.5))
```
fails with
```
TypeError: float() argument must be a string or a real number, not 'slice'
```

### What did you expect to happen?

In v2022.3, this yields the correct sliced selection. Also, in v2022.6 this works for Multiindices without float-Values
```python
da = xr.DataArray(np.random.rand(4), {'x': np.arange(4)})
da = da.assign_coords(y=('x', np.arange(4)))
da = da.assign_coords(z=('x', np.arange(4) + 4))
da.set_index(x=[""y"", ""z""]).sel(y=slice(None, 2), z=slice(5, None))
```
(only that the resulting coordinates look a bit weird, containing `slice`s). Also, the sliced selection for a regular float-based index works in v2202.6
```python
da = xr.DataArray(np.random.rand(4), {'x': np.linspace(0, 1, 4)})
da.sel(x=slice(None, 0.5))
```

### Minimal Complete Verifiable Example

```Python
import numpy as np
import xarray as xr

da = xr.DataArray(np.random.rand(4), {'x': np.arange(4)})
da = da.assign_coords(y=('x', np.linspace(0, 1, 4)))
da = da.assign_coords(z=('x', np.arange(4) + 4))
da.set_index(x=[""y"", ""z""]).sel(y=slice(None, 0.5))
```


### MVCE confirmation

- [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
- [X] Complete example — the example is self-contained, including all data and the text of any traceback.
- [X] Verifiable example — the example copy & pastes into an IPython prompt or [Binder notebook](https://mybinder.org/v2/gh/pydata/xarray/main?urlpath=lab/tree/doc/examples/blank_template.ipynb), returning the result.
- [X] New issue — a search of GitHub Issues suggests this is not a duplicate.

### Relevant log output

```Python
File c:\mambaforge\envs\dev\lib\site-packages\xarray\core\dataarray.py:1420, in DataArray.sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
   1310 def sel(
   1311     self: T_DataArray,
   1312     indexers: Mapping[Any, Any] = None,
   (...)
   1316     **indexers_kwargs: Any,
   1317 ) -> T_DataArray:
   1318     """"""Return a new DataArray whose data is given by selecting index
   1319     labels along the specified dimension(s).
   1320 
   (...)
   1418     Dimensions without coordinates: points
   1419     """"""
-> 1420     ds = self._to_temp_dataset().sel(
   1421         indexers=indexers,
   1422         drop=drop,
   1423         method=method,
   1424         tolerance=tolerance,
...
    197     # see https://github.com/pydata/xarray/issues/5727
--> 198     value = np.asarray(value, dtype=dtype)
    199 return value

TypeError: float() argument must be a string or a real number, not 'slice'
```


### Anything else we need to know?

Maybe related to #6836

### Environment

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.10.5 | packaged by conda-forge | (main, Jun 14 2022, 06:57:19) [MSC v.1929 64 bit (AMD64)]
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 142 Stepping 12, GenuineIntel
byteorder: little
LC_ALL: None
LANG: de_DE.UTF-8
LOCALE: ('de_DE', 'cp1252')
libhdf5: None
libnetcdf: None

xarray: 2022.6.0
pandas: 1.4.3
numpy: 1.23.1
scipy: 1.8.1
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: 3.5.2
cartopy: None
seaborn: 0.11.2
numbagg: None
fsspec: None
cupy: None
pint: 0.19.2
sparse: None
flox: None
numpy_groupies: None
setuptools: 63.2.0
pip: 22.2
conda: None
pytest: 7.1.2
IPython: 8.4.0
sphinx: 4.5.0

</details>
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