ci: prevent segfaults in ci_visibility Python 3.8 tests

[brettlangdon]

This change prevents a segfault coming from zope.interface when running the ci_visibility test suite under Python 3.8

This issue was found during the PR #12243. It is unclear why that PR surfaces the issue, but the extracted segfault traceback is showing zope.interface._compat._c_optimizations_available as the trigger for the segfault.

The fix to work around this issue is to set the PURE_PYTHON=1 environment variable which will tell zope.interface to not use this c extension at all.

Example segfault from CI

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

riotfile.py                                                             @DataDog/apm-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: brettlangdon/ci.viz.segfaults
Commit report: 2902682
Test service: dd-trace-py

✅ 0 Failed, 130 Passed, 1184 Skipped, 4m 25.98s Total duration (26m 28.86s time saved)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 12.67%. Comparing base (eebffbf) to head (2902682).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12291   +/-   ##
=======================================
  Coverage   12.67%   12.67%           
=======================================
  Files        1376     1376           
  Lines      135399   135399           
=======================================
  Hits        17162    17162           
  Misses     118237   118237           

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