Update Altair snapshot - #19488

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There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 4.6.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 6ef5a17ad831be80c3e63911b77fa9f8acfcbf50

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #19488: Update Altair snapshot'

4. Push to a named branch:

git push YOURFORK 4.6.x:auto-backport-of-pr-19488-on-4.6.x

5. Create a PR against branch 4.6.x, I would have named this PR:

"Backport PR #19488 on branch 4.6.x (Update Altair snapshot)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

This seems to explain why the vega version may change over time: https://github.com/vega/altair/blob/86932854b2ca32b0e01b17f880e0dab938e9d949/altair/utils/html.py#L45

Which seems to be the default route taken here in JupyterLab since there is no dedicated renderer for Vega 6 (yet).