[io] fix: implement python3.9 specific plugin loading

[AndreyMarkinPPC]

In 3.9 loading entry_points is different than 3.10+

[codecov-commenter]

Codecov Report

❌ Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.31%. Comparing base (af99b02) to head (8ea68e4).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
libs/io/garf_io/writer.py	42.85%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #119      +/-   ##
==========================================
- Coverage   87.50%   87.31%   -0.19%     
==========================================
  Files          57       57              
  Lines        2625     2634       +9     
==========================================
+ Hits         2297     2300       +3     
- Misses        328      334       +6     

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