Migrate to modern threading interface

[emmanuel-ferdman]

PR Summary

This small PR resolves the threading library warnings, which you can find in the CI logs:

/home/runner/work/sentry-python/sentry-python/tests/conftest.py:608: DeprecationWarning: setDaemon() is deprecated, set the daemon attribute instead
    mock_server_thread.setDaemon(True)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.63%. Comparing base (7f8571c) to head (926b4f1).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4452      +/-   ##
==========================================
- Coverage   80.68%   80.63%   -0.05%     
==========================================
  Files         142      142              
  Lines       15986    15986              
  Branches     2732     2732              
==========================================
- Hits        12898    12891       -7     
- Misses       2230     2238       +8     
+ Partials      858      857       -1     

see 5 files with indirect coverage changes

[sl0thentr0py]

ty!