build(deps): update docker.io/alpine docker tag to v3.21.3

Author: renovate[bot]

Dockerfile

@@ -22,7 +22,7 @@ RUN chmod +x parca-load
 
 # https://github.com/hadolint/hadolint/issues/861
 # hadolint ignore=DL3029
-FROM --platform="${TARGETPLATFORM:-linux/amd64}"  docker.io/alpine:3.21.2@sha256:56fa17d2a7e7f168a043a2712e63aed1f8543aeafdcee47c58dcffe38ed51099 AS runner
+FROM --platform="${TARGETPLATFORM:-linux/amd64}"  docker.io/alpine:3.21.3@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c AS runner
 
 USER 65533