reno: Update master for unmaintained/2024.1

Update the 2024.1 release notes configuration to build from
unmaintained/2024.1.

Change-Id: I02a5088563ec81b900d95c2db1c6988f3b3c1372
Signed-off-by: OpenStack Release Bot <infra-root@openstack.org>
Generated-By: openstack/project-config:roles/copy-release-tools-scripts/files/release-tools/change_reno_branch_to_unmaintained.sh

Author: openstackadmin

releasenotes/source/2024.1.rst

@@ -3,4 +3,4 @@
 ===========================
 
 .. release-notes::
-   :branch: stable/2024.1
+   :branch: unmaintained/2024.1