omni: change branch refs to 13.0

Change-Id: I07996ea076918aae2868a3e8c82d3920d9ab5b0f
diff --git a/utils/fork_github.sh b/utils/fork_github.sh
index e869325..c11d3d7 100755
--- a/utils/fork_github.sh
+++ b/utils/fork_github.sh
@@ -13,7 +13,7 @@
 ##
 USERNAME=<INSERT USER>
 TOKEN=<INSERT TOKEN>
-BRANCH=android-12.1
+BRANCH=android-13.0
 GERRIT=gerrit.omnirom.org
 GITHUB_ORG=omnirom