Update release notes

Author: Tyler-lc

RELEASE_NOTES.rst

@@ -47,6 +47,7 @@ All changes
 
 - Document the :ref:`minimum version of Java <install-java>` required for :class:`ixmp.JDBCBackend <ixmp.backend.jdbc.JDBCBackend>` (:pull:`962`).
 - Improve type hinting (:pull:`963`).
+- Fix capitalization in in auxiliary_settings.gms to enable GDX output file compression on MacOS and Linux. (:pull:`965`) 
 
 .. _v3.11.1: