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
782440858,MDU6SXNzdWU3ODI0NDA4NTg=,4784,Opening a tiff with scale_factor/add_offset attrs then saving as zarr and opening causes a UFuncTypeError,53100696,closed,0,,,4,2021-01-08T22:45:21Z,2024-02-06T10:40:15Z,2024-02-06T10:40:14Z,NONE,,,,"<!-- Please include a self-contained copy-pastable example that generates the issue if possible.

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**What happened**:
When opening a geotiff that has `scale_factor` and `add_offset` metadata and then saving it as a zarr the `scale_factor` and `add_offset` attributes are [loaded](https://github.com/pydata/xarray/blob/5296ed18272a856d478fbbb3d3253205508d1c2d/xarray/backends/rasterio_.py#L280) and then saved as strings. When the resulting zarr is opened xarray attempts to [apply](https://github.com/pydata/xarray/blob/569a4da18229aed391886ef768132f3d6d64fb30/xarray/coding/variables.py#L245) the `scale_factor` and `add_offset` attributes, but raises an exception because they are of type `<U32`.
```
/srv/conda/envs/notebook/lib/python3.8/site-packages/xarray/coding/variables.py in _scale_offset_decoding(data, scale_factor, add_offset, dtype)
    218     data = np.array(data, dtype=dtype, copy=True)
    219     if scale_factor is not None:
--> 220         data *= scale_factor
    221     if add_offset is not None:
    222         data += add_offset

UFuncTypeError: Cannot cast ufunc 'multiply' output from dtype('<U32') to dtype('float32') with casting rule 'same_kind'
```
**What you expected to happen**:
1. `scale_factor` and `add_offset` are converted to floats and applied when the tiff is opened
2. When attempting to apply `scale_factor` and `add_offset` attributes, check their types and/or cast them to floats.

**Minimal Complete Verifiable Example**:

```python
import xarray as xr
img = xr.open_rasterio('https://hlssa.blob.core.windows.net/hls/S30/HLS.S30.T10TET.2019001.v1.4_04.tif')
img.to_dataset(name='img', promote_attrs=True).to_zarr('./test.zarr', mode='w')
xr.open_zarr('./test.zarr').persist()
```

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

**Environment**:

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

INSTALLED VERSIONS
------------------
commit: None
python: 3.8.6 | packaged by conda-forge | (default, Dec 26 2020, 05:05:16) 
[GCC 9.3.0]
python-bits: 64
OS: Linux
OS-release: 5.4.0-1034-azure
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: 1.2.0
numpy: 1.19.5
scipy: 1.6.0
netCDF4: 1.5.5.1
pydap: None
h5netcdf: 0.8.1
h5py: 2.10.0
Nio: None
zarr: 2.6.1
cftime: 1.3.0
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.8
cfgrib: None
iris: None
bottleneck: None
dask: 2020.12.0
distributed: 2020.12.0
matplotlib: 3.3.3
cartopy: 0.18.0
seaborn: None
numbagg: None
pint: None
setuptools: 49.6.0.post20201009
pip: 20.3.3
conda: None
pytest: 6.2.1
IPython: 7.19.0
sphinx: None


</details>
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