[requirements] Transition 2023.1 Antelope to Unmaintained

This branch reached the end of its official stable maintained period,
hence this patch transition stable/2023.1 branch to Unmaintained. (For
details about Unmaintained state please see: [1][2])

The transitions is as follows:
- tip of the stable/2023.1 branch is tagged with 2023.1-eom tag
- unmaintained/2023.1 branch will be cut from 2023.1-eom tag
- stable/2023.1 branch will be deleted

Note:
- there will no longer be official releases off of 2023.1 branch after
  this transition
- backports can be pushed to unmaintained/2023.1 branch
- openstack-unmaintained-core (or <project>-unmaintained-core groups if
  such exists) have the rights to merge patches

Important: please +1 if the team is ready for us to proceed with this
transition, or -1 if there are any final 2023.1 Antelope stable release
with backports currently in flight that we should wait for. For the
latter case, please propose a final 2023.1 Antelope stable release
patch, and rebase this patch on top of that, with the latest commit
hash of stable/2023.1.

The planned transition deadline was October 30th, 2024 [3] last week,
so please approve this patch as soon as possible if the project is
ready for the transition.

[1] https://docs.openstack.org/project-team-guide/stable-branches.html#unmaintained
[2] https://governance.openstack.org/tc/resolutions/20230724-unmaintained-branches.html
[3] https://releases.openstack.org

Change-Id: I7f97a91fa092d0179cd2200d352f92515b0d0169

deliverables/antelope/requirements.yaml

@@ -11,3 +11,10 @@ branches:
   - name: stable/2023.1
     location:
       openstack/requirements: e7d3312a31340af93dc2f35d03f622272007f69d
+  - name: unmaintained/2023.1
+    location: 2023.1-eom
+releases:
+  - version: 2023.1-eom
+    projects:
+      - repo: openstack/requirements
+        hash: 838389db5a48e9bc6450e1ea51c4b36dd3d3f88f