Add change note for #1914.

Fixes #1914

docs/changes/1910.misc

+Use a more modern setuptools build backend. There have also been some
+other build related changes:
+
+- Enable memory leak checking for Python 3.11.
+..
+  TODO: Uncomment this once done
+  - Stop using the deprecated 'DEF' construct in Cython files. See https://github.com/cython/cython/issues/4310

setup.py

@@ -13,6 +13,15 @@ from setuptools import Extension, setup
 from setuptools import find_packages
 
 
+# -*- coding: utf-8 -*-
+#
+# We import other files that are siblings of this file as modules. In
+# the past, setuptools guaranteed that this directory was on the path
+# (typically, the working directory) but in a PEP517 world, that's no
+# longer guaranteed to be the case. setuptools provides a PEP517
+# backend (``setuptools.build_meta:__legacy__``) that *does* guarantee
+# that, and we used it for a long time. But downstream packagers have begun
+# complaining about using it. So we futz with the path ourself.
 sys.path.insert(0, os.path.dirname(__file__))
 
 from _setuputils import read