wrong compiler version in CI for gcc

[MaxBetzDLR]

Bug description

gcc/gxx-11 gets installed, while only version 9 and 10 are used for building and testing

Version

Github (CI, Actions, etc.)

To reproduce

Bug found in .github/actions/linux-build/action.yml

Relevant log output

No response

Add any relevant information, e.g. used compiler, screenshots.

No response

Checklist

• [X] Attached labels, especially loc:: or model:: labels.
• [X] Linked to project