Fix setuptools license deprecation warnings in setup.py

[adev-code]

When building botocore with python -m build -w, setuptools generates deprecation warnings:
License classifier warning: The License :: OSI Approved :: Apache Software License classifier is deprecated in favor of SPDX license expressions.

This PR fixes setuptools license deprecation warnings that appear during wheel building as described above.

Changes Made

• Removed deprecated License :: OSI Approved :: Apache Software License from classifiers
• Added license="Apache-2.0" field using SPDX identifier

Testing

• Verified python -m build -w runs without warnings
• Confirmed package installation still works correctly
• All existing functionality preserved

Resolves: #3434

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.17%. Comparing base (bbed2c0) to head (c2a02dc).
⚠️ Report is 219 commits behind head on develop.
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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3575      +/-   ##
===========================================
+ Coverage    93.13%   93.17%   +0.03%     
===========================================
  Files           68       68              
  Lines        15336    15411      +75     
===========================================
+ Hits         14283    14359      +76     
+ Misses        1053     1052       -1     

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