update mainline branch reminder from T to U

tweak the script to have the right udc-mainline-prod warning.
Note that this need goes away once mainline is built from main branch
instead of a separate mainline branch.

Bug: 319262694
Test: repo upload
Change-Id: Ic4e409a45559ec6bb687deccb7b72b1899b73ef2
diff --git a/tools/mainline_hook_project.sh b/tools/mainline_hook_project.sh
index 1cc3b2b..d58143e 100755
--- a/tools/mainline_hook_project.sh
+++ b/tools/mainline_hook_project.sh
@@ -16,8 +16,8 @@
 
 
 # tunables
-DEV_BRANCH=master
-MAINLINE_BRANCH=tm-mainline-prod
+DEV_BRANCH=main
+MAINLINE_BRANCH=udc-mainline-prod
 
 ###
 RED=$(tput setaf 1)