Exception not handled in widgetlock()

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## Describe the issue
I want to use a selector `matplotlib.widgets.RectangleSelector` , it is incompatible with zoom and pan
So I try to call widget lock to prevent user from using zoom in the same time.

minimum code:
```python
%matplotlib ipympl
import matplotlib.pyplot as plt
fig,ax = plt.subplots()
ax.plot([0,1],[0,1])
fig.canvas.widgetlock(ax) # get the widget lock
```
if you then hit the zoom or pan matplotlib button, which also try to get the lock, you get
```
ValueError Traceback (most recent call last)
File ~/spike/venvOW/lib/python3.9/site-packages/ipympl/backend_nbagg.py:279, in Canvas._handle_message(self, object, content, buffers)
276 self.manager.handle_json(content)
278 else:
--> 279 self.manager.handle_json(content)

...

File ~/spike/venvOW/lib/python3.9/site-packages/matplotlib/widgets.py:42, in LockDraw.__call__(self, o)
40 """Reserve the lock for *o*."""
41 if not self.available(o):
---> 42 raise ValueError('already locked')
43 self._owner = o

ValueError: already locked

```

Alternatively, I could use the right click for the selector, but I have not found a way to restrict zoom and pan to left click only.

## Versions

```
3.9.7 (default, Sep 16 2021, 13:09:58)
[GCC 7.5.0]
ipympl version: 0.8.8
Selected Jupyter core packages...
IPython : 8.0.1
ipykernel : 6.9.1
ipywidgets : 7.6.5
jupyter_client : 7.1.2
jupyter_core : 4.9.2
jupyter_server : 1.13.5
jupyterlab : not installed
nbclient : 0.5.11
nbconvert : 6.4.2
nbformat : 5.1.3
notebook : 6.4.8
qtconsole : 5.2.2
traitlets : 5.1.1
```

Riproduci il problema con l’esempio minimo di Jupyter, quindi ispeziona ipympl/backend_nbagg.py e matplotlib/widgets.py in corrispondenza della gestione del lock del widget mostrata nel traceback. Conferma il comportamento previsto quando un’operazione di zoom o panoramica tenta di acquisire un lock occupato e aggiungi una copertura che dimostri che l’interazione non produce più un ValueError non gestito.

Scritto dal modello di indicizzazione a partire dal testo della issue.