Unable to access ipympl from JupyterLab due to Error displaying widget: model not found

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## Describe the issue

I am running an example code to access ipympl from Jupyter Lab on GCP/Linux.

```
%matplotlib widget
import matplotlib.pyplot as plt
import numpy as np
import sys
"ipympl" in sys.modules
True

# Testing matplotlib interactions with a simple plot
fig = plt.figure()
plt.plot(np.sin(np.linspace(0, 20, 100)));

Error displaying widget: model not found

```

## Versions

```
Paste the command output here.

3.8.10 (default, Mar 13 2023, 10:26:41)
[GCC 9.4.0]
ipympl version: 0.9.3
Selected Jupyter core packages...
IPython : 8.12.0
ipykernel : 6.13.0
ipywidgets : 8.0.6
jupyter_client : 8.2.0
jupyter_core : 5.3.0
jupyter_server : 2.5.0
jupyterlab : 3.6.3
nbclient : 0.7.4
nbconvert : 7.3.1
nbformat : 5.8.0
notebook : 6.5.4
qtconsole : not installed
traitlets : 5.9.0
Known nbextensions:
config dir: /usr/local/etc/jupyter/nbconfig
notebook section
jupyter-matplotlib/extension enabled
- Validating: OK
jupyter_resource_usage/main enabled
- Validating: OK
nbdime/index enabled
- Validating: OK
jupyter-js-widgets/extension enabled
- Validating: OK
tree section
jupyter_server_proxy/tree enabled
- Validating: OK
JupyterLab v3.6.3
/usr/local/share/jupyter/labextensions
jupyterlab_pygments v0.2.2 enabled OK (python, jupyterlab_pygments)
dask-labextension v6.1.0 enabled OK (python, dask_labextension)
nbdime-jupyterlab v2.2.0 enabled OK
jupyter-matplotlib v0.11.3 enabled OK
jupyterlab-nvdashboard v0.8.0 enabled OK (python, jupyterlab_nvdashboard)
@jupyterlab/git v0.41.0 enabled OK (python, jupyterlab-git)
@jupyter-widgets/jupyterlab-manager v5.0.7 enabled OK (python, jupyterlab_widgets)
@jupyterhub/jupyter-server-proxy v4.0.0 enabled OK
@jupyter-server/resource-usage v0.7.2 enabled OK (python, jupyter-resource-usage)
@jupyter-lsp/jupyterlab-lsp v4.1.0 enabled OK (python, jupyterlab-lsp)
@elyra/code-snippet-extension v3.15.0 enabled OK
@elyra/script-debugger-extension v3.15.0 enabled OK
@elyra/python-editor-extension v3.15.0 enabled OK
@elyra/metadata-extension v3.15.0 enabled OK
@elyra/pipeline-editor-extension v3.15.0 enabled OK
@elyra/code-viewer-extension v3.15.0 enabled OK
@elyra/theme-extension v3.15.0 enabled OK
@elyra/r-editor-extension v3.15.0 enabled OK
@elyra/scala-editor-extension v3.15.0 enabled OK

Other labextensions (built into JupyterLab)
app dir: /usr/local/share/jupyter/lab

Disabled extensions:
@jupyterlab/launcher-extension (all plugins)
```

Reproduce the reported example beginning with `%matplotlib widget` in JupyterLab 3.6.3, using the listed ipympl, ipywidgets, and Jupyter package versions. Check the JupyterLab widget integration and the enabled `jupyter-matplotlib` and `@jupyter-widgets/jupyterlab-manager` extensions first. Done means the sine plot renders as an interactive widget without the “model not found” error.

Written by the indexing model from the issue text.