feat: Update Vega-Lite to 5.20.1

[binste]

Compared to 5.19, it includes the new parameters react and tickBandPaddingInner.

Edit: I'll need to update the tests next. Note to myself to also update NOTES_FOR_MAINTAINERSE.md to mention this.

[jonmmease]

@binste, feel free to update the tests/vegalite/v5/test_api.py::test_to_url test to to only check the start of the URL (the way we do when checking PNG/SVG images). Testing that the full URL is accurate is really vl-convert's responsibility, so I don't think we need to check the whole thing here, especially since it breaks on every Vega-Lite update.

[binste]

Good point! Changed it