Cast the column to the correct type before assigning values

[quant12345]

This PR removes many warnings: FutureWarning: Setting an item of incompatible dtype is deprecated and will raise an error in a future version of pandas.

I see in warnings (3.12, 2) it too, but as an error:
ERROR pandapower/test/plotting/test_geo.py - FutureWarning: Setting an item of incompatible dtype is deprecated and will raise an error in a future version of pandas. Value '[-2, -3]' has dtype incompatible with int32, please explicitly cast to a compatible dtype first.

Update 09.09.2024

What was done:
mv_oberrhein.py:76
Column net.trafo["tap_pos"] has values ​​nan and this is float type, so astype("float64").

from_ppc.py:336
branch_lookup.loc[is_impedance, "element"] = idx_impedance
although all masks is_impedance [False False False False False False False] and
idx_impedance represents an empty list, which changes the type from int64 to float64, so astype("float64").

create.py:5990
moved line 5991 up to convert column to correct type before assignment

geo.py:556, test_iec60909_4.py:470
the value to set is a string or None, so the type is object

grid_modification.py:1217-1219
Since val can contain both string and numeric values, I define the column type based on the values.

grid_modification.py:1232-1233, 1399-1400, 1621-1622
Casting values to column type net[table]"element"]

[quant12345]

Tests with changes to grid_modification.py fail. Will close PR. Maybe reopen.

Update 09.09.2024: Figured out why there was an error, see grid_modification.py:1217-1219 above.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.00%. Comparing base (a044a46) to head (5808955).
Report is 9 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2371   +/-   ##
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  Coverage    76.00%   76.00%           
========================================
  Files          282      282           
  Lines        32945    32950    +5     
========================================
+ Hits         25040    25045    +5     
  Misses        7905     7905           

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