TT#124273 Fix py.test-3 junit family deprecation warning

Running the test suite on bullseye/sid generates the following warning:

  ,---
  ====================================================================== warnings summary ================================================================>
  /usr/lib/python3/dist-packages/_pytest/junitxml.py:446
    /usr/lib/python3/dist-packages/_pytest/junitxml.py:446: PytestDeprecationWarning: The 'junit_family' default value will change to 'xunit2' in pytest 6>
      https://docs.pytest.org/en/stable/deprecations.html#junit-family-default-value-change-to-xunit2
    for more information.
      _issue_warning_captured(deprecated.JUNIT_XML_DEFAULT_FAMILY, config.hook, 2)

  -- Docs: https://docs.pytest.org/en/stable/warnings.html
  `---

Adding a config file and setting the junit family explicitly fixes
silences the warning.

Change-Id: I929b0c4630769ed263be0aeb8776a0233954e599

tests/pytest.ini

@@ -0,0 +1,2 @@
+[pytest]
+junit_family=xunit2