Fix broken JupyterWidget chart by pinning Vega

[jonmmease]

Closes #3268

[binste]

Thanks @jonmmease!

Does this mean that we continuously need to bump Vega versions? Do you know of a good way to test when this is resolved so we can stop pinning it again? Could you add a note to NOTES_FOR_MAINTAINERS.md that this version should be kept up-to-date?

[mattijn]

Was wondering the same. How does this interfere with:

alt.VEGAEMBED_VERSION, alt.VEGA_VERSION  # alt.VEGALITE_VERSION, 

('6', '5')

[jonmmease]

I'll take another look at this when I update Vega-Lite. It might work to unpin the version and switch to the latest from https://esm.sh/.

[jonmmease]

I updated the esm.sh URL to use the same vega embed, vega, and vega-lite versions as the rest of Altair. I added a note to NOTES_FOR_MAINTAINERS with instructions for updating this URL when we update vega-lite.