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
1061868498,I_kwDOAMm_X84_StPS,6021,Variable name becomes lowercase when saving to GCS with `to_zarr`,23640870,closed,0,,,2,2021-11-24T00:57:21Z,2021-11-24T17:16:32Z,2021-11-24T17:16:32Z,NONE,,,,"**What happened**:

A variable name was transformed to lowercase when saving a dataset to GCS with `ds.to_zarr`

**What you expected to happen**:

Variable name should remain unchanged.

**Minimal Complete Verifiable Example**:

```python
import xarray as xr
ds = xr.Dataset({'TEMPERATURE': xr.DataArray(data=[0, 1], dims=['x'])})
ds.to_zarr('gs://bucket/test.zarr')
print(xr.open_dataset('gs://bucket/test.zarr', engine='zarr').data_vars)
```
and the last line prints
```
Data variables:
    temperature  (x) int64 ...
```

It also shows up as lowercase if I do `gsutil ls gs://bucket/test.zarr`.

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

Does not happen if writing the dataset to a local path or if I pass `fsspec.get_mapper('gs://bucket/test.zarr')` to `ds.to_zarr`. 

Should I even be able to use `ds.to_zarr` with a string GCS path if I do not pass any `storage_options` ?

**Environment**:

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

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.10 | packaged by conda-forge | (default, Feb 19 2021, 16:07:37) 
[GCC 9.3.0]
python-bits: 64
OS: Linux
OS-release: 5.4.0-1057-gcp
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: C.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.10.5
libnetcdf: 4.6.3

xarray: 0.19.0
pandas: 1.0.1
numpy: 1.19.4
scipy: 1.5.4
netCDF4: 1.5.5
pydap: None
h5netcdf: 0.8.1
h5py: 2.10.0
Nio: None
zarr: 2.7.0
cftime: 1.2.1
nc_time_axis: 1.2.0
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2021.11.1
distributed: 2021.11.1
matplotlib: 3.2.2
cartopy: 0.19.0.post1
seaborn: None
numbagg: None
pint: 0.15
setuptools: 49.6.0.post20210108
pip: 20.2.4
conda: 4.10.1
pytest: 6.0.1
IPython: 7.29.0
sphinx: 3.2.1

Also:
fsspec: 2021.06.0
gcsfs: 2021.06.0
</details>

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