Add changelog entry for 2a93d6b

Author: mnaberez

CHANGES.rst

@@ -1,6 +1,10 @@
 4.3.0.dev0 (Next Release)
 -------------------------
 
+- Fixed a bug where the poller would not unregister a closed
+  file descriptor under some circumstances, which caused excessive
+  polling, resulting in higher CPU usage.  Patch by aftersnow.
+
 - On Python 3.8 and later, ``setuptools`` is no longer a runtime
   dependency.  Patch by Ofek Lev.