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
1030811490,I_kwDOAMm_X849cO9i,5878,problem appending to zarr on GCS when using json token ,48723181,open,0,,,16,2021-10-19T23:01:57Z,2022-11-15T22:04:21Z,,NONE,,,,"<!-- Please include a self-contained copy-pastable example that generates the issue if possible.

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**What happened**:
Appending a toy dataset to an existing zarr store in GCS along the time dimension leaves the store unchanged. 

**What you expected to happen**:
The store to double in length, because I was appending a dataset with a length of 3 in the time dimension, to another dataset of the same size.

**Minimal Complete Verifiable Example**:
To reproduce fully you will need the token, but maybe people can try using their own token. 
```python
import fsspec
import xarray as xr
import json
import gcsfs


## define a mapper to the ldeo-glaciology bucket
### needs a token
with open('../secrets/ldeo-glaciology-bc97b12df06b.json') as token_file:
    token = json.load(token_file)

mapper = fsspec.get_mapper('gs://ldeo-glaciology/append_test/test5', mode='w', token=token)

## define two simple datasets
ds0 = xr.Dataset({'temperature': (['time'],  [50, 51, 52])}, coords={'time': [1, 2, 3]})
ds1 = xr.Dataset({'temperature': (['time'],  [53, 54, 55])}, coords={'time':  [4, 5, 6]})

## write the fist to bucket
ds0.to_zarr(mapper)
## append the second to the same zarr store
ds1.to_zarr(mapper, mode='a', append_dim='time')

## load the zarr store
ds_both = xr.open_zarr(mapper)

## this is 3, indicating that the append did not work 
len(ds_both.time)
```

**Anything else we need to know?**:
It works as expected if you instead write and append to the pangeo scratch bucket, i.e if you replace 
```
with open('../secrets/ldeo-glaciology-bc97b12df06b.json') as token_file:
    token = json.load(token_file)

mapper = fsspec.get_mapper('gs://ldeo-glaciology/append_test/test5', mode='w', token=token)
``` 
with 
```
mapper = fsspec.get_mapper('gs://pangeo-scratch/jkingslake/append_test/test3', mode='w', token=None)
``` 

It also works as expected if I write and append to a local zarr. 

Thanks for your help!


**Environment**:
https://us-central1-b.gcp.pangeo.io/
<details><summary>Output of <tt>xr.show_versions()</tt></summary>

INSTALLED VERSIONS
------------------
commit: None
python: 3.8.6 | packaged by conda-forge | (default, Jan 25 2021, 23:21:18) 
[GCC 9.3.0]
python-bits: 64
OS: Linux
OS-release: 5.4.129+
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: C.UTF-8
LANG: C.UTF-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.6
libnetcdf: 4.7.4

xarray: 0.16.2
pandas: 1.2.1
numpy: 1.20.0
scipy: 1.6.0
netCDF4: 1.5.5.1
pydap: installed
h5netcdf: 0.8.1
h5py: 3.1.0
Nio: None
zarr: 2.6.1
cftime: 1.4.1
nc_time_axis: 1.2.0
PseudoNetCDF: None
rasterio: 1.2.0
cfgrib: 0.9.8.5
iris: None
bottleneck: 1.3.2
dask: 2021.01.1
distributed: 2021.01.1
matplotlib: 3.3.4
cartopy: 0.18.0
seaborn: None
numbagg: None
pint: 0.16.1
setuptools: 49.6.0.post20210108
pip: 20.3.4
conda: None
pytest: None
IPython: 7.20.0
sphinx: 3.4.3

</details>
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