finalization: use same repo branch during dry-run

Teach step-*.sh to re-use the same branch name if running in dry-run
mode. This is useful for running the steps sequentially: if using
different branch names, each 'repo start' will undo the changes created
during the previous step-*.sh.

Bug: 323940469
Test: croot && build/tools/finalization/step-1.sh --dry-run && build/tools/finalization/step-2.sh --dry-run
Ignore-AOSP-first: VIC finalization happens outside AOSP
Change-Id: I720f294f6abf5a8b276bb30f8c531fcbea749b76
diff --git a/tools/finalization/command-line-options.sh b/tools/finalization/command-line-options.sh
index 1c5df46..d9397c2 100644
--- a/tools/finalization/command-line-options.sh
+++ b/tools/finalization/command-line-options.sh
@@ -2,7 +2,7 @@
 eval set -- "$ARGV"
 while true; do
     case "$1" in
-        --dry-run) repo_upload_dry_run_arg="--dry-run"; shift ;;
+        --dry-run) repo_upload_dry_run_arg="--dry-run"; repo_branch="finalization-dry-run"; shift ;;
         *) break
     esac
 done