refactor(python): invoke pip as python -m pip

[scop]

• https://snarky.ca/why-you-should-use-python-m-pip/
• https://pip.pypa.io/en/stable/user_guide/#using-pip-from-your-program

Caveat: untested.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01% ⚠️

Comparison is base (90a41f1) 87.68% compared to head (62e8f5c) 87.68%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #792      +/-   ##
==========================================
- Coverage   87.68%   87.68%   -0.01%     
==========================================
  Files         130      130              
  Lines       11394    11392       -2     
==========================================
- Hits         9991     9989       -2     
  Misses       1403     1403              

Files Changed	Coverage Δ
src/plugins/core/python.rs	60.60% <100.00%> (-0.48%)	⬇️

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