Drop support for Python 3.9

[mr-c]

• Make one more Python 3.9 supporting release when the final release of Python 3.9.x happens at the end of this month (2025-10)
• then merge this PR

[codecov]

Codecov Report

❌ Patch coverage is 42.85714% with 424 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.62%. Comparing base (88ad2a6) to head (d2b5156).

Files with missing lines	Patch %	Lines
cwl_utils/cwl_v1_1_expression_refactor.py	13.09%	67 Missing and 6 partials ⚠️
cwl_utils/cwl_v1_2_expression_refactor.py	24.70%	57 Missing and 7 partials ⚠️
cwl_utils/cwl_v1_0_expression_refactor.py	38.09%	41 Missing and 11 partials ⚠️
cwl_utils/expression.py	43.85%	23 Missing and 9 partials ⚠️
cwl_utils/parser/utils.py	63.21%	25 Missing and 7 partials ⚠️
cwl_utils/parser/cwl_v1_0_utils.py	46.55%	24 Missing and 7 partials ⚠️
cwl_utils/parser/cwl_v1_1_utils.py	46.55%	24 Missing and 7 partials ⚠️
cwl_utils/parser/cwl_v1_2_utils.py	46.55%	24 Missing and 7 partials ⚠️
cwl_utils/inputs_schema_gen.py	27.58%	17 Missing and 4 partials ⚠️
cwl_utils/utils.py	16.00%	21 Missing ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #378      +/-   ##
==========================================
+ Coverage   34.56%   34.62%   +0.05%     
==========================================
  Files          30       30              
  Lines       35382    35417      +35     
  Branches     9555     9538      -17     
==========================================
+ Hits        12231    12262      +31     
- Misses      20266    20275       +9     
+ Partials     2885     2880       -5     

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