tac: re-declare ARG VERSION in tacchaind go-builder stage

Pre-FROM ARG VERSION is not visible inside build stages; compose passes
VERSION as a build arg but git checkout expanded empty without a stage-level
re-declaration.

Co-authored-by: Cursor <cursoragent@cursor.com>

tac/tacchaind.Dockerfile

@@ -3,6 +3,8 @@ ARG VERSION=v1.6.0
 
 FROM golang:1.23.8-alpine3.21 AS go-builder
 
+ARG VERSION
+
 RUN apk add --no-cache \
     ca-certificates \
     build-base \