Ignore pytest 6.2.0 resource warnings under py 3.8

Refs:
* #1897
* https://docs.pytest.org/en/stable/usage.html#unraisable
* pytest-dev/pytest#5299

pytest.ini

@@ -33,6 +33,13 @@ addopts =
 doctest_optionflags = ALLOW_UNICODE ELLIPSIS
 filterwarnings =
     error
+
+    # pytest>=6.2.0 under Python 3.8:
+    # Ref: https://docs.pytest.org/en/stable/usage.html#unraisable
+    # Ref: https://github.com/pytest-dev/pytest/issues/5299
+    ignore:Exception ignored in. <socket.socket fd=-1, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6>:pytest.PytestUnraisableExceptionWarning:_pytest.unraisableexception
+    ignore:Exception ignored in. <_io.FileIO .closed.>:pytest.PytestUnraisableExceptionWarning:_pytest.unraisableexception
+
     ignore:Use cheroot.test.webtest:DeprecationWarning
     ignore:This method will be removed in future versions.*:DeprecationWarning
     ignore:Unable to verify that the server is bound on:UserWarning