Bump the docker group across 3 directories with 1 update

Bumps the docker group with 1 update in the /images/cfssl/rootfs directory: alpine.
Bumps the docker group with 1 update in the /images/nginx/rootfs directory: alpine.
Bumps the docker group with 1 update in the /rootfs directory: alpine.


Updates `alpine` from 3.20 to 3.21

Updates `alpine` from 3.20 to 3.21

Updates `alpine` from 3.20 to 3.21

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

Signed-off-by: dependabot[bot] <support@github.com>

images/cfssl/rootfs/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 RUN echo "@testing https://dl-cdn.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories
 RUN apk update \

images/nginx/rootfs/Dockerfile

@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-FROM alpine:3.20 as builder
+FROM alpine:3.21 as builder
 
 COPY . /
 
@@ -21,7 +21,7 @@ RUN apk update \
   && /build.sh
 
 # Use a multi-stage build
-FROM alpine:3.20
+FROM alpine:3.21
 
 ENV PATH=$PATH:/usr/local/luajit/bin:/usr/local/nginx/sbin:/usr/local/nginx/bin
 

rootfs/Dockerfile-chroot

@@ -23,7 +23,7 @@ RUN apk update \
   && apk upgrade \
   && /chroot.sh
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 ARG TARGETARCH
 ARG VERSION