Bump alpine from 3.20.3 to 3.21.0 in the docker group

Bumps the docker group with 1 update: alpine.


Updates `alpine` from 3.20.3 to 3.21.0

---
updated-dependencies:
- dependency-name: alpine
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: docker
...

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

Dockerfile

@@ -7,7 +7,7 @@ RUN go test ./...
 ARG version=dev
 RUN go build -ldflags "-X main.Version=$version" -o /bin/ecr-image-sync
 
-FROM alpine:3.20.3
+FROM alpine:3.21.0
 
 COPY --from=build /bin/ecr-image-sync /usr/local/bin/ecr-image-sync
 ENTRYPOINT ["ecr-image-sync"]