pandas deprecation fix for read_json

[vogt31337]

Hi,

since pandas version 2.10 read_json from literal (string) is deprecated. The message is really annoying and messes up logfiles.
Therefore this patch, which will wrap a string into an StringIO object (as recommmended by the pandas people). Probably it will also be faster?

BR

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (5592ba1) 78.97% compared to head (9b529f7) 78.97%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2125   +/-   ##
========================================
  Coverage    78.97%   78.97%           
========================================
  Files          214      214           
  Lines        26718    26722    +4     
========================================
+ Hits         21101    21105    +4     
  Misses        5617     5617           

Files Changed	Coverage Δ
pandapower/io_utils.py	75.33% <100.00%> (+0.12%)	⬆️

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