Fix: use newer Alpine Linux Docker base image

- Alpine 3.18.4 is too old to build Go 1.24

Server/Dockerfile-binary-builder

@@ -1,4 +1,4 @@
-FROM alpine:3.18.4
+FROM alpine:3.21.3
 
 ENV GOLANG_VERSION 1.24.3
 ENV GOLANG_SRC_URL https://golang.org/dl/go$GOLANG_VERSION.src.tar.gz