Fix rendering of code-cell within sphinx_design tab groups

[VeckoTheGecko]

Fixes #723

Changes:

• Updates the rendering
• Adds sphinx_design as a test dependency
• Run pytest --regen-all to regenerate the data files

The changes in the data files are not visually different (mainly OEF newline, and updated hashes).

I hope that the reading update is correct! (it was LLM driven, but the change fixes the doc issue I was having).

[VeckoTheGecko]

Hmmm, just saw

MyST-NB/myst_nb/core/read.py

Lines 398 to 403 in 3c93e0c

	"Found an unexpected `code-cell` or `raw-cell` directive. "
	"Either this file was not converted to a notebook, "
	"because Jupytext header content was missing, "
	"or the `code-cell` was not converted, because it is nested. "
	"See https://myst-nb.readthedocs.io/en/latest/authoring/text-notebooks.html "
	"for more information."

Maybe my PR and issue is out of scope for this project

[VeckoTheGecko]

I'm going to close this. I'm not confident in this fix and don't know if the original issue is actually intentional behaviour