drop_sel returns KeyError for abbreviated dates

What happened?

for a dataframe with a detailed timestamp coordinate (2022-03-11T13:50:50.551314000)

da.sel(time="2022-03-11") works but da.drop_sel(time="2022-03-11") results in a KeyError

What did you expect to happen?

i expect drop_sel() to work with the same inputs as sel()

Minimal Complete Verifiable Example

import numpy as np
import xarray as xr
times = np.array(['2022-03-03T13:50:49.548072000', '2022-03-11T13:50:50.551314000',
                  '2022-03-12T13:44:35.547024000', '2022-03-13T12:18:48.015182000'],
                  dtype='datetime64[ns]')

da = xr.DataArray(np.arange(4), dims="time", coords={"time": times})
da.drop_sel(time='2022-03-11')

A workaround is to use the exact datestring:

da.drop_sel(time='2022-03-11T13:50:50.551314000')

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[4], line 1
----> 1 da.drop_sel(time='2022-03-11')

File ~/.local/envs/xvec/lib/python3.11/site-packages/xarray/core/dataarray.py:3105, in DataArray.drop_sel(self, labels, errors, **labels_kwargs)
   3102 if labels_kwargs or isinstance(labels, dict):
   3103     labels = either_dict_or_kwargs(labels, labels_kwargs, "drop")
-> 3105 ds = self._to_temp_dataset().drop_sel(labels, errors=errors)
   3106 return self._from_temp_dataset(ds)

File ~/.local/envs/xvec/lib/python3.11/site-packages/xarray/core/dataset.py:5292, in Dataset.drop_sel(self, labels, errors, **labels_kwargs)
   5290     except KeyError:
   5291         raise ValueError(f"dimension {dim!r} does not have coordinate labels")
-> 5292     new_index = index.drop(labels_for_dim, errors=errors)
   5293     ds = ds.loc[{dim: new_index}]
   5294 return ds

File ~/.local/envs/xvec/lib/python3.11/site-packages/pandas/core/indexes/base.py:6934, in Index.drop(self, labels, errors)
   6932 if mask.any():
   6933     if errors != "ignore":
-> 6934         raise KeyError(f"{list(labels[mask])} not found in axis")
   6935     indexer = indexer[~mask]
   6936 return self.delete(indexer)

KeyError: "['2022-03-11'] not found in axis"

Anything else we need to know?

related to https://github.com/pydata/xarray/issues/6605#issuecomment-1126139617

Environment

(xarray: 2023.3.0)

Start with DataArray.drop_sel in xarray/core/dataarray.py and Dataset.drop_sel in xarray/core/dataset.py, following the index.drop call shown in the traceback. Reproduce the issue with the provided MVCE and compare abbreviated-date behavior with sel(); done means drop_sel removes the matching timestamp without raising KeyError.