chore(deps): update alpine docker tag to v3.21 (k8s-test-tools/dockerfile) (#973)

Co-authored-by: IK Renovate Bot <[email protected]>

Author: ivankatliarchuk

Diff for: k8s-test-tools/Dockerfile

@@ -4,7 +4,7 @@
 # Run:
 # docker run --rm -it test-image /bin/bash
 ###
-FROM alpine:3.20 as builder
+FROM alpine:3.21 as builder
 
 # renovate: datasource=github-releases depName=kubernetes/kubectl
 ARG K8S_VERSION=v1.30.1