Upgrade causes error when using multiple addSeriesAsDrilldown()

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### Describe the bug
As part of the Angular tech stack upgrade, due to dependency to Ivy, I was forced to upgrade the Highcharts and Highcharts-Angular as follows:
highcharts: 6.2.0 >> 9.3.3
highcharts-angular: 2.10.0 >> 3.1.2
This resulted in a bug which does not allow calling addSeriesAsDrilldown() multiple times in a look. It worked in the previous version.

### Expected behavior
Expected the drill down continue to work with multiple series.

### Demo
Please provide live demo of the problem or provide any other way to recreate the problem.

#### Steps required to recreate the problem in the demo:
1. ...

### Setup used
- NodeJS version ...
- Angular version ...
- TypeScript version ...
etc.