test: use venv in w3c trace context test script

[pichlermarc]

Which problem is this PR solving?

Tests are currently failing (see here, probably due to some changes that don't allow the use of pip install with an externally managed environment, like the global one that's supposed to be managed by the system and requires packages to be installed via apt on Ubuntu 24.04). This PR makes the test script use a venv instead to avoid this error.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Local testing (I tested this on Ubuntu 24.04 and it was also happening there)
• workflow here on this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.27%. Comparing base (7ed67f9) to head (7d5202e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5071      +/-   ##
==========================================
+ Coverage   93.26%   93.27%   +0.01%     
==========================================
  Files         317      317              
  Lines        8195     8195              
  Branches     1641     1641              
==========================================
+ Hits         7643     7644       +1     
+ Misses        552      551       -1     

see 1 file with indirect coverage changes