fix

Dockerfile.eshop.backend

@@ -2,7 +2,8 @@
 # Separate lightweight Go build, sharing the same module and internal packages as the main backend.
 
 # Build stage
-FROM golang:1.24.5-bullseye AS builder
+ARG GO_IMAGE_TAG=1.25.8-bookworm
+FROM golang:${GO_IMAGE_TAG} AS builder
 
 WORKDIR /app