Update docker.io/postgres Docker tag to v18

.gitea/workflows/render-manifests.yaml

@@ -90,7 +90,7 @@ jobs:
           fi
 
           echo ">> Directories to Render:"
-          RENDER_DIR=$(printf "%s\n" "${RENDER_DIR[@]}" | sort -u)
+          RENDER_DIR=(printf "%s\n" "${RENDER_DIR[@]}" | sort -u)
           echo "$RENDER_DIR"
           echo "-----"