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
1285001323,I_kwDOAMm_X85Ml5Br,6728,open_dataset segfaults when opening hdf5 with array of strings,352673,closed,0,,,8,2022-06-26T18:48:04Z,2022-06-27T16:10:21Z,2022-06-27T16:10:20Z,NONE,,,,"### What happened?

An attempt to open *non* netCDF4 hdf5 file with `xarray.open_dataset` results in a segmentation fault.

### What did you expect to happen?

Code execute and not die a horrible death.

### Minimal Complete Verifiable Example

```Python
import h5py
import numpy as np
from xarray import open_dataset

filename = ""foobar.h5""

with h5py.File(filename, ""w"") as fp:
    fp[""test""] = np.array([""foo"", ""bar"", ""baz""], dtype=""|S3"")

with open_dataset(filename, engine=""netcdf4"") as ds:
    print(""yay"")
```


### 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
$ python3 -Wd -X faulthandler bug.py 
Fatal Python error: Segmentation fault

Current thread 0x00007f2283947740 (most recent call first):
  File ""/home/xarth/codes/xarthisius/xarray/xarray/backends/netCDF4_.py"", line 106 in _getitem
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/indexing.py"", line 816 in explicit_indexing_adapter
  File ""/home/xarth/codes/xarthisius/xarray/xarray/backends/netCDF4_.py"", line 93 in __getitem__
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/indexing.py"", line 527 in __array__
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/variable.py"", line 250 in _as_array_or_item
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/variable.py"", line 510 in values
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/variable.py"", line 337 in data
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/common.py"", line 1866 in contains_cftime_datetimes
  File ""/home/xarth/codes/xarthisius/xarray/xarray/core/common.py"", line 1875 in _contains_datetime_like_objects
  File ""/home/xarth/codes/xarthisius/xarray/xarray/conventions.py"", line 345 in decode_cf_variable
  File ""/home/xarth/codes/xarthisius/xarray/xarray/conventions.py"", line 521 in decode_cf_variables
  File ""/home/xarth/codes/xarthisius/xarray/xarray/backends/store.py"", line 27 in open_dataset
  File ""/home/xarth/codes/xarthisius/xarray/xarray/backends/netCDF4_.py"", line 567 in open_dataset
  File ""/home/xarth/codes/xarthisius/xarray/xarray/backends/api.py"", line 495 in open_dataset
  File ""/home/xarth/codes/xarthisius/yt/bug.py"", line 10 in <module>
Segmentation fault (core dumped)
```


### Anything else we need to know?

This regression was introduced in #6489

### Environment

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.9.5 (default, Nov 23 2021, 15:27:38) 
[GCC 9.3.0]
python-bits: 64
OS: Linux
OS-release: 5.4.0-121-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: en_US.utf8
LANG: en_US.utf8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.2
libnetcdf: 4.9.0

xarray: 2022.3.1.dev60+g5f01c115
pandas: 1.4.3
numpy: 1.23.0
scipy: 1.9.0rc1
netCDF4: 1.6.0
pydap: None
h5netcdf: None
h5py: 3.7.0
Nio: None
zarr: None
cftime: 1.6.0
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2022.6.1
distributed: None
matplotlib: 3.5.2
cartopy: None
seaborn: None
numbagg: None
fsspec: 2022.5.0
cupy: None
pint: None
sparse: None
setuptools: 44.0.0
pip: 20.0.2
conda: None
pytest: 7.1.2
IPython: 8.4.0
sphinx: None

</details>
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