Fixed typo in override-checkout branch for stable/2023.1

Change-Id: I9cab114176217e82b9f981135bdc8ed152d57988
diff --git a/zuul.d/stable-jobs.yaml b/zuul.d/stable-jobs.yaml
index d399556..ed5cd31 100644
--- a/zuul.d/stable-jobs.yaml
+++ b/zuul.d/stable-jobs.yaml
@@ -39,7 +39,7 @@
     name: tempest-slow-2023-1
     parent: tempest-slow-py3
     nodeset: openstack-two-node-jammy
-    override-checkout: stable/2023-1
+    override-checkout: stable/2023.1
 
 - job:
     name: tempest-full-enforce-scope-new-defaults-zed