Bump chart.js from 2.9.3 to 2.9.4 in /web-ui

Bumps [chart.js](https://github.com/chartjs/Chart.js) from 2.9.3 to 2.9.4.
- [Release notes](https://github.com/chartjs/Chart.js/releases)
- [Commits](https://github.com/chartjs/Chart.js/compare/v2.9.3...v2.9.4

)

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