tests: update pytest 6.2.1 and fix test_python_alreadyset_in_destructor (#2741)

* Update pytest to 6.2.1 in tests/requirements.txt

* Pin pytest to last supported version for 3.5

* Suppress PytestUnraisableExceptionWarning and use sys.__unraisablehook__ instead of sys.unraisablehook

* Fix filterwarnings mark on old pytest and old Python versions

* Cleanup ignore_pytest_unraisable_warning decorator

tests/requirements.txt

@@ -3,6 +3,7 @@ numpy==1.16.6; python_version<"3.6" and sys_platform!="win32"
 numpy==1.18.0; platform_python_implementation=="PyPy" and sys_platform=="darwin" and python_version>="3.6"
 numpy==1.19.3; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version>="3.6" and python_version<"3.10"
 pytest==4.6.9; python_version<"3.5"
-pytest==5.4.3; python_version>="3.5"
+pytest==6.1.2; python_version=="3.5"
+pytest==6.2.1; python_version>="3.6"
 scipy==1.2.3; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version<"3.6"
 scipy==1.5.2; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version>="3.6" and python_version<"3.9"

tests/test_exceptions.py

@@ -50,13 +50,24 @@ def test_python_call_in_catch():
     assert d["good"] is True
 
 
+def ignore_pytest_unraisable_warning(f):
+    unraisable = "PytestUnraisableExceptionWarning"
+    if hasattr(pytest, unraisable):  # Python >= 3.8 and pytest >= 6
+        dec = pytest.mark.filterwarnings("ignore::pytest.{}".format(unraisable))
+        return dec(f)
+    else:
+        return f
+
+
+@ignore_pytest_unraisable_warning
 def test_python_alreadyset_in_destructor(monkeypatch, capsys):
     hooked = False
     triggered = [False]  # mutable, so Python 2.7 closure can modify it
 
     if hasattr(sys, "unraisablehook"):  # Python 3.8+
         hooked = True
-        default_hook = sys.unraisablehook
+        # Don't take `sys.unraisablehook`, as that's overwritten by pytest
+        default_hook = sys.__unraisablehook__
 
         def hook(unraisable_hook_args):
             exc_type, exc_value, exc_tb, err_msg, obj = unraisable_hook_args