tests: make use of incorporated Pytest subtests

https://github.com/pytest-dev/pytest-subtests?tab=readme-ov-file#important

> This plugin has been integrated directly into pytest 9.0, so the
  plugin itself will no longer be maintained and the repository will be
  archived.

Fixes: #948
Signed-off-by: Stanislav Levin <slev@altlinux.org>

Author: stanislavlevin

setup.cfg

@@ -62,13 +62,12 @@ rst =
 test = 
     docutils>=0.18.1
     coverage
-    pytest
+    pytest>=9
     pytest-xdist
     hypothesis
     cython-test-exception-raiser
     bs4
     Sphinx
-    pytest-subtests
     setuptools
 
 mypy =