Remove git clean -fxd from build_python target

[Copilot]

build_python runs git clean -fxd before building the wheel, which deletes all untracked files in sdk/python/. When generated Python SDK files aren't tracked by git, this wipes them out and produces an empty wheel.

• Removed git clean -fxd from the build_python Makefile target
• Added ./venv/ to the existing rm -rf to clean stale virtualenvs from prior builds

The existing rm -rf ./bin/ ../python.bin/ already ensures a clean build directory — git clean was redundant at best, destructive at worst.

# Before
cd sdk/python && \
    git clean -fxd && \
    rm -rf ./bin/ ../python.bin/ && cp -R . ../python.bin && mv ../python.bin ./bin && \

# After
cd sdk/python && \
    rm -rf ./bin/ ../python.bin/ ./venv/ && cp -R . ../python.bin && mv ../python.bin ./bin && \

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[github-actions]

Does the PR have any schema changes?

Looking good! No breaking changes found.
No new resources/functions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.86%. Comparing base (bd8b0f5) to head (28e64e4).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4573   +/-   ##
=======================================
  Coverage   62.86%   62.86%           
=======================================
  Files          90       90           
  Lines       10936    10936           
=======================================
  Hits         6875     6875           
  Misses       3416     3416           
  Partials      645      645           

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[pulumi-bot]

This PR has been shipped in release v3.15.0.