Drop Python 3.9 support

[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 76.76162% with 155 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.57%. Comparing base (0037b6d) to head (762afd2).

Files with missing lines	Patch %	Lines
cwltool/cwlprov/provenance_profile.py	7.93%	54 Missing and 4 partials ⚠️
cwltool/main.py	61.22%	11 Missing and 8 partials ⚠️
cwltool/subgraph.py	42.42%	14 Missing and 5 partials ⚠️
cwltool/argparser.py	72.72%	6 Missing and 6 partials ⚠️
cwltool/load_tool.py	77.35%	8 Missing and 4 partials ⚠️
cwltool/workflow.py	60.00%	5 Missing and 1 partial ⚠️
cwltool/process.py	92.85%	3 Missing and 2 partials ⚠️
cwltool/secrets.py	78.26%	0 Missing and 5 partials ⚠️
cwltool/validate_js.py	84.61%	2 Missing and 2 partials ⚠️
cwltool/checker.py	88.00%	2 Missing and 1 partial ⚠️
... and 8 more

❗ There is a different number of reports uploaded between BASE (0037b6d) and HEAD (762afd2). Click for more details.

HEAD has 6 uploads less than BASE

Flag	BASE (0037b6d)	HEAD (762afd2)
	18	12

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2159      +/-   ##
==========================================
- Coverage   85.16%   77.57%   -7.59%     
==========================================
  Files          46       46              
  Lines        8332     8358      +26     
  Branches     1954     1951       -3     
==========================================
- Hits         7096     6484     -612     
- Misses        771     1355     +584     
- Partials      465      519      +54     

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