deps: update alpine docker tag to v3.21 (#817)

Author: renovate[bot]

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.20
+FROM alpine:3.21
 RUN apk add --no-cache ca-certificates bash
 COPY hcloud-cloud-controller-manager /bin/hcloud-cloud-controller-manager
 ENTRYPOINT ["/bin/hcloud-cloud-controller-manager"]

dev/Dockerfile

@@ -14,7 +14,7 @@ ARG SKAFFOLD_GO_GCFLAGS
 ENV GOCACHE=/cache
 RUN --mount=type=cache,target="/cache" go build -gcflags="$SKAFFOLD_GO_GCFLAGS" -o hcloud-cloud-controller-manager.bin github.com/hetznercloud/hcloud-cloud-controller-manager
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 RUN apk add --no-cache \
     bash \