Silence a warning specific to Python 3.14

The existing Python 3.13 filterwarning is copied and adapted for the
Python 3.14 syntax

Author: mr-c

docs/changelog-fragments.d/767.contrib.rst

@@ -0,0 +1,3 @@
+Tests: copied and adapted Python 3.13 filter warning for Python 3.14, to match
+the new syntax
+-- by :user:`mr-c`.

pytest.ini

@@ -61,6 +61,8 @@ filterwarnings =
   # FIXME: which exposed a possible race condition in test_conn test cleanup.
   # Ref: https://github.com/cherrypy/cheroot/issues/734
   ignore:Exception ignored in. <function IOBase.__del__:pytest.PytestUnraisableExceptionWarning
+  # Python 3.14 version of the above
+  ignore:Exception ignored while calling deallocator <function IOBase.__del__ at:pytest.PytestUnraisableExceptionWarning
 
 # https://docs.pytest.org/en/stable/usage.html#creating-junitxml-format-files
 junit_duration_report = call