fix incorrect handeling of dimensions in data processing

[Luca-Ben-Herrmann]

We fixed the incorrect handling of the dimensions in the data processing of the readout frequency optimization experiment.
Before fix: http://login.qrccluster.com:9000/fm9khE2vSOe4PD3Az8uywQ==
After fix: http://login.qrccluster.com:9000/viE48NXFS6ySplY9syja9Q==

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.31%. Comparing base (bc7a7ba) to head (ebddece).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1081      +/-   ##
==========================================
+ Coverage   97.30%   97.31%   +0.01%     
==========================================
  Files         124      124              
  Lines        9884     9884              
==========================================
+ Hits         9618     9619       +1     
+ Misses        266      265       -1     

Flag	Coverage Δ
unittests	97.31% <100.00%> (+0.01%)	⬆️

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Files with missing lines	Coverage Δ
...tocols/readout_optimization/resonator_frequency.py	99.00% <100.00%> (ø)

... and 2 files with indirect coverage changes