[charts] Fix outline color

[alexfauquette]

On bar chart, the outline was taking the color of the bar.

Here we fix the color to:

• black in light mode
• white in dark mode

[mui-bot]

Deploy preview: https://deploy-preview-19752--material-ui-x.netlify.app/

Bundle size report

Bundle	Parsed size	Gzip size
@mui/x-data-grid	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-pro	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-premium	0B(0.00%)	0B(0.00%)
@mui/x-charts	🔺+90B(+0.03%)	🔺+21B(+0.02%)
@mui/x-charts-pro	🔺+94B(+0.02%)	🔺+13B(+0.01%)
@mui/x-charts-premium	🔺+90B(+0.02%)	🔺+10B(+0.01%)
@mui/x-date-pickers	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers-pro	0B(0.00%)	0B(0.00%)
@mui/x-tree-view	0B(0.00%)	0B(0.00%)
@mui/x-tree-view-pro	0B(0.00%)	0B(0.00%)

Details of bundle changes

Generated by 🚫 dangerJS against 5b69308

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #19752 will not alter performance

_{Comparing alexfauquette:fix-outline-color (5b69308) with master (5154e31)¹}

Summary

✅ 12 untouched

Footnotes

1. No successful run was found on master (d3c0b88) during the generation of this report, so 5154e31 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩