tests: cleanup and ci hardening (#2397)

* tests: refactor and cleanup

* refactor: more consistent

* tests: vendor six

* tests: more xfails, nicer system

* tests: simplify to info

* tests: suggestions from @YannickJadoul and @bstaletic

* tests: restore some pypy tests that now pass

* tests: rename info to env

* tests: strict False/True

* tests: drop explicit strict=True again

* tests: reduce minimum PyTest to 3.1

tests/test_methods_and_attributes.py

@@ -1,5 +1,8 @@
 # -*- coding: utf-8 -*-
 import pytest
+
+import env  # noqa: F401
+
 from pybind11_tests import methods_and_attributes as m
 from pybind11_tests import ConstructorStats
 
@@ -257,8 +260,8 @@ def test_property_rvalue_policy():
     assert os.value == 1
 
 
-# https://bitbucket.org/pypy/pypy/issues/2447
-@pytest.unsupported_on_pypy
+# https://foss.heptapod.net/pypy/pypy/-/issues/2447
+@pytest.mark.xfail("env.PYPY")
 def test_dynamic_attributes():
     instance = m.DynamicClass()
     assert not hasattr(instance, "foo")
@@ -299,8 +302,8 @@ def test_dynamic_attributes():
         assert cstats.alive() == 0
 
 
-# https://bitbucket.org/pypy/pypy/issues/2447
-@pytest.unsupported_on_pypy
+# https://foss.heptapod.net/pypy/pypy/-/issues/2447
+@pytest.mark.xfail("env.PYPY")
 def test_cyclic_gc():
     # One object references itself
     instance = m.DynamicClass()