Additional iconv transliteration tests

[PhilinTv]

Based on initial #1057
This helps isolate odd iconv transliteration behavior, to make it clear when Propel2 is at fault and when failed tests stems from incorrect/unsupported locale configuration.

⚠️ Iconv transliteration tests may fail if the system locale is C or if libiconv version is inconsistent. To ensure stability, use en_US.UTF-8 locale when running tests.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.03%. Comparing base (353266c) to head (47df675).
⚠️ Report is 7 commits behind head on master.
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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2053      +/-   ##
============================================
+ Coverage     68.56%   74.03%   +5.46%     
- Complexity     8073     8075       +2     
============================================
  Files           232      232              
  Lines         24569    24575       +6     
============================================
+ Hits          16845    18193    +1348     
+ Misses         7724     6382    -1342     

Flag	Coverage Δ
5-max	74.03% <ø> (+5.46%)	⬆️
7.4	74.03% <ø> (+5.46%)	⬆️
agnostic	?
mysql	69.85% <ø> (?)
pgsql	69.90% <ø> (?)
sqlite	67.84% <ø> (?)

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