Code Insights: Fix line chart hover areas distribution

Created by: vovakulikov

Closes https://github.com/sourcegraph/sourcegraph/issues/38919

Test plan

• Open https://k8s.sgdev.org/insights/dashboards/ZGFzaGJvYXJkOnsiSWRUeXBlIjoiY3VzdG9tIiwiQXJnIjo3MjY0Nzl9
• Make sure that the hover point does make sense based on the mouse cursor position

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.