Bump alpine from 3.21.2 to 3.21.3 in /docker

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] <support@github.com>

Author: dependabot[bot]

docker/Dockerfile

@@ -14,7 +14,7 @@
 #  limitations under the License.
 #
 
-FROM alpine:3.21.2@sha256:56fa17d2a7e7f168a043a2712e63aed1f8543aeafdcee47c58dcffe38ed51099 AS staging_area
+FROM alpine:3.21.3@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c AS staging_area
 
 RUN apk --no-cache add openjdk21-jdk openjdk21-jmods
 
@@ -68,7 +68,7 @@ RUN jlink \
     --strip-java-debug-attributes \
     --output "$JAVA_MINIMAL"
 
-FROM alpine:3.21.2@sha256:56fa17d2a7e7f168a043a2712e63aed1f8543aeafdcee47c58dcffe38ed51099
+FROM alpine:3.21.3@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c
 
 ENV JAVA_HOME=/opt/java-minimal
 ENV PATH="$PATH:$JAVA_HOME/bin"