chore(deps): update image alpine to v3.21.0 (#101)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.goreleaser.Dockerfile

@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile:1
 
 ## Setup stage
-FROM alpine:3.20.3@sha256:1e42bbe2508154c9126d48c2b8a75420c3544343bf86fd041fb7527e017a4b4a as builder
+FROM alpine:3.21.0@sha256:21dc6063fd678b478f57c0e13f47560d0ea4eeba26dfc947b2a4f81f686b9f45 as builder
 
 RUN apk --no-cache add ca-certificates tzdata
 RUN addgroup --gid 65532 kani && \