fix periodic snapshot upgrade env merge

scripts/soak/run_soak.sh

@@ -416,10 +416,11 @@ max_existing_run_index() {
   local run_name
   local numeric_part
   shopt -s nullglob
-  for run_dir in "$RUNS_ROOT"/run_[0-9][0-9][0-9][0-9]; do
+  for run_dir in "$RUNS_ROOT"/run_*; do
     [[ -d "$run_dir" ]] || continue
     run_name="$(basename "$run_dir")"
     numeric_part="${run_name#run_}"
+    [[ "$numeric_part" =~ ^[0-9]+$ ]] || continue
     if (( 10#$numeric_part > max_index )); then
       max_index=$((10#$numeric_part))
     fi