omni: change branch refs to 13.0

Change-Id: I07996ea076918aae2868a3e8c82d3920d9ab5b0f
diff --git a/utils/aosp-merge.sh b/utils/aosp-merge.sh
index d3c4587..519401c 100755
--- a/utils/aosp-merge.sh
+++ b/utils/aosp-merge.sh
@@ -24,7 +24,7 @@
 
 branch_name=${ref}"-merge"
 
-branch_current="android-12.1"
+branch_current="android-13.0"
 
 cd ../../../