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
800678839,MDU6SXNzdWU4MDA2Nzg4Mzk=,4859,Unicode strings unexpectedly transformed to byte strings upon `open_dataset`,38673295,closed,0,,,7,2021-02-03T20:34:27Z,2021-11-20T17:58:34Z,2021-11-20T17:58:34Z,NONE,,,,"**What happened**:

Unicode coordinates convert to bytes after saving/loading with `h5netcdf` backend. This results with the practically unusable dataset (bytes != string). 

**What you expected to happen**:

Load the string as a string. 

**Minimal Complete Verifiable Example**:

```python
coils = np.array([""A"", ""B"", ""C"", ""D"", ""E""])
data = np.array([1 + 1j, 1 + 2j, 3j, 4j, 6j])

test_ds = xr.Dataset()
test_ds.coords[""coils""] = coils
test_ds[""data""] = (""coils"", data)
test_ds

> <xarray.Dataset>
> Dimensions:  (coils: 5)
> Coordinates:
>  * coils    (coils) <U1 'A' 'B' 'C' 'D' 'E'
> Data variables:
>    data     (coils) complex128 (1+1j) (1+2j) 3j 4j 6j



test_ds.to_netcdf(""test.nc"", engine=""h5netcdf"")
del test_ds
test_ds = xr.open_dataset(""test.nc"", engine=""h5netcdf"")
test_ds

> <xarray.Dataset>
> Dimensions:  (coils: 5)
> Coordinates:
>   * coils    (coils) object b'A' b'B' b'C' b'D' b'E'
> Data variables:
>     data     (coils) complex128 ...

```

**Anything else we need to know?**:

The issue may be related to #1638. 

**Environment**:

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

INSTALLED VERSIONS
------------------
commit: None
python: 3.8.6 | packaged by conda-forge | (default, Oct  7 2020, 19:08:05) 
[GCC 7.5.0]
python-bits: 64
OS: Linux
OS-release: 5.4.0-65-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: cs_CZ.UTF-8
LOCALE: cs_CZ.UTF-8
libhdf5: 1.10.5
libnetcdf: 4.6.3

xarray: 0.16.2
pandas: 1.1.5
numpy: 1.19.4
scipy: 1.5.3
netCDF4: 1.5.5
pydap: None
h5netcdf: 0.8.1
h5py: 3.1.0
Nio: None
zarr: None
cftime: 1.3.0
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: 1.3.2
dask: 2020.12.0
distributed: 2020.12.0
matplotlib: 3.3.3
cartopy: None
seaborn: 0.11.0
numbagg: None
pint: 0.16.1
setuptools: 49.6.0.post20201009
pip: 20.3.3
conda: None
pytest: 6.2.1
IPython: 7.19.0
sphinx: None

</details>
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/4859/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue