FIX: issue 1939 fix grpc Terminal not set as reference causing random failure on SIwave

[svandenb-dev]

This PR is addressing issue #1939 found by a user where some methods have hard coded is_ref=False. These terminals are functional but according to the users, this is causing random failure when importing EDB in Siwave. Some voltage source or Current source might be ignored during import. Making sure that negative terminal is always set as reference is resolving this failure.

closes #1939

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.91%. Comparing base (5cbae21) to head (d79e04f).
⚠️ Report is 53 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1944      +/-   ##
==========================================
+ Coverage   70.20%   70.91%   +0.70%     
==========================================
  Files         261      263       +2     
  Lines       42416    42884     +468     
==========================================
+ Hits        29779    30411     +632     
+ Misses      12637    12473     -164     

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[ecoussoux-ansys]

Thanks for the changes that cover everything the user had reported 👍
I just left 2 minor comments if you'd like to check.

Also, for your info: On line 970 of source_excitations.py, there is a call to PadstackInstanceTerminal.create() very similar to the one you updated in _create_terminal_on_pins() (line 1252) which (I believe) is explicitly for creating negative terminal but where is_ref is still set to False. Just mentioning in case it would make sense to update this parameter in this other call as well.