Google Colab issue

まだ誰も着手していません。

The problem in encountered in current Google Collab version. If I use `ipympl` the easiest way - the code worked about two months ago:
```
!pip install ipympl
from google.colab import output
output.enable_custom_widget_manager()

%matplotlib ipympl
```

I get an Error message:

> Key backend: 'module://ipympl.backend_nbagg' is not a valid value for backend; supported values are ['gtk3agg', 'gtk3cairo', 'gtk4agg', 'gtk4cairo', 'macosx', 'nbagg', 'notebook', 'qtagg', 'qtcairo', 'qt5agg', 'qt5cairo', 'tkagg', 'tkcairo', 'webagg', 'wx', 'wxagg', 'wxcairo', 'agg', 'cairo', 'pdf', 'pgf', 'ps', 'svg', 'template', 'module://ipykernel.pylab.backend_inline', 'inline']

However, If I do

`%matplotlib --list`

I get:
> Available matplotlib backends: ['tk', 'gtk', 'gtk3', 'gtk4', 'wx', 'qt4', 'qt5', 'qt6', 'qt', 'osx', 'nbagg', 'notebook', 'agg', 'svg', 'pdf', 'ps', 'inline', 'ipympl', 'widget']

Reproduce the issue's notebook snippet in the current Google Colab environment, including the ipympl installation and output.enable_custom_widget_manager() call. Compare the backend listed by `%matplotlib --list` with the backend accepted by Matplotlib and inspect the resulting compatibility path. Done means the cause is identified and either the integration works in current Colab or the limitation is documented.

索引モデルが issue の本文から書いたものです。