build: bump alpine from 3.21.2 to 3.21.3

Bumps alpine from 3.21.2 to 3.21.3.

---
updated-dependencies:
- dependency-name: alpine
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Dockerfile.alpine

@@ -24,7 +24,7 @@ RUN set -eux; \
 	go env | grep -E 'OS=|ARCH=|ARM=|AMD64='; \
     go build -ldflags "-X main.buildVersion=${DOCKER_GEN_VERSION}" -o docker-gen ./cmd/docker-gen
 
-FROM alpine:3.21.2
+FROM alpine:3.21.3
 
 ARG DOCKER_GEN_VERSION
 ENV DOCKER_GEN_VERSION=${DOCKER_GEN_VERSION} \