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
442063346,MDU6SXNzdWU0NDIwNjMzNDY=,2949,xr.DataArray.to_series returns a (mutable) view,881019,open,0,,,8,2019-05-09T06:02:23Z,2020-11-16T21:58:10Z,,NONE,,,,"#### Code Sample, a copy-pastable example if possible
```python
import numpy as np
import pandas as pd
import xarray as xr

dates = pd.date_range('01-Jan-2019', '01-Jan-2020', name='forward_date')[:-1]
s = pd.Series(np.random.randn(dates.size), dates)
array = xr.DataArray.from_series(s)
```
```python
In [52]: array
Out[52]: 
<xarray.DataArray (forward_date: 365)>
array([ 0.511149, -1.009054, -0.098397, ...,  0.496596,  1.435346,  0.21206 ])
Coordinates:
  * forward_date  (forward_date) datetime64[ns] 2019-01-01 ... 2019-12-31

In [53]: array.to_series().index.name
Out[53]: 'forward_date'

In [54]: array.to_series().index.name = 'peristent!!!'

In [55]: array.to_series().index.name
Out[55]: 'peristent!!!'

In [56]: array.get_index('forward_date')
Out[56]: 
DatetimeIndex(['2019-01-01', '2019-01-02', '2019-01-03', '2019-01-04',
               '2019-01-05', '2019-01-06', '2019-01-07', '2019-01-08',
               '2019-01-09', '2019-01-10',
               ...
               '2019-12-22', '2019-12-23', '2019-12-24', '2019-12-25',
               '2019-12-26', '2019-12-27', '2019-12-28', '2019-12-29',
               '2019-12-30', '2019-12-31'],
              dtype='datetime64[ns]', name='peristent!!!', length=365, freq='D')
```

#### Problem description
IMHO Setting `index.name` on the returned series shouldn't affect the original `DataArray` - i.e. every call to `array.to_series().index.name` should return `forward_date` irrespective of any mutating operations performed on the returned series.

#### Expected Output

#### Output of ``xr.show_versions()``

<details>

```python
In [48]: xr.show_versions()
Traceback (most recent call last):

  File ""<ipython-input-48-6f391305f2fe>"", line 1, in <module>
    xr.show_versions()

  File ""C:\Users\dhirschf\envs\dev\lib\site-packages\xarray\util\print_versions.py"", line 84, in show_versions
    sys_info.extend(netcdf_and_hdf5_versions())

  File ""C:\Users\dhirschf\envs\dev\lib\site-packages\xarray\util\print_versions.py"", line 75, in netcdf_and_hdf5_versions
    libhdf5_version = h5py.__hdf5libversion__

AttributeError: module 'h5py' has no attribute '__hdf5libversion__'
```
</details>
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