fix: drone job

.drone.yml

@@ -50,14 +50,14 @@ steps:
   - name: wait_for_postgres
     image: docker.io/library/postgres:17.6
     commands:
-      # Wait for postgres to become available
+      # Wait for postgres to become available (POSIX-compatible)
       - |
-        for i in {1..20}; do
+        i=0
+        while [ $i -lt 20 ]; do
           if pg_isready -h postgres -U postgres; then
             exit 0
-          else
-            true
           fi
+          i=$((i + 1))
           sleep 2
         done
         echo "Postgres did not become available, aborting."