1022 wrong compiler version in ci for gcc

[MaxBetzDLR]

Changes and Information

Please briefly list the changes (main added features, changed items, or corrected bugs) made:

• Use gcc/gxx-11 in CI
• Update Readme

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Closes #1022

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.23%. Comparing base (bcfa8d3) to head (9e6b4b6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1023      +/-   ##
==========================================
- Coverage   96.51%   96.23%   -0.29%     
==========================================
  Files         128      128              
  Lines       10538    10852     +314     
==========================================
+ Hits        10171    10443     +272     
- Misses        367      409      +42     

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[reneSchm]

Just a minor change in the Readme, the rest looks good to me.

The change in abm_braunchschweig makes a lot of sense - I just removed the save_result_result in another branch as it was effectively unused, but stopping the entire ensemble because a singular output failed is likely not desirable. This here is better.