Fix pie chart xaxis labels extraction for chartjs

Problem/Motivation

I have a bar chart that displays correctly, using Chart.js.
When I switch the chart to pie, I'm getting a JS error:

Uncaught TypeError: n.reduce is not a function
    o plugin.legend.js:564
    <anonymous> plugin.legend.js:556
    _fitCols plugin.legend.js:205
    _fitCols plugin.legend.js:204
    fit plugin.legend.js:150
    update plugin.legend.js:89
    ss core.layouts.js:187
    update core.layouts.js:417
    _updateLayout core.controller.js:634
    update core.controller.js:528
    An core.controller.js:211
    attach charts_chartjs.js:39
    attach charts_chartjs.js:21
    attachBehaviors drupal.js:166
    attachBehaviors drupal.js:162
    <anonymous> drupal.init.js:32
    listener drupal.init.js:20

It seems related to this: https://stackoverflow.com/questions/78842674/chartjs-pie-chart-with-reac...

And it seems the same issue happened with HighCharts: #3239687: Fix pie chart xaxis labels extraction for highcharts →

I'll provide a fix similar to that issue.