Update golang:1.21-alpine Docker digest to a6a7f1f

Dockerfile

@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1@sha256:ac85f380a63b13dfcefa89046420e1781752bab202122f8f50032edf31be0021
-FROM golang:1.21-alpine@sha256:51a7800206bc7b276a9d62a7229cdede7b1e0f45ec28259ed44c1603c6cda1e7 AS build-env
+FROM golang:1.21-alpine@sha256:a6a7f1fcf12f5efa9e04b1e75020931a616cd707f14f62ab5262bfbe109aa84a AS build-env
 RUN mkdir -p /go/src/confluence-gardner
 
 # Copy the module files first and then download the dependencies. If this