Bump alpine from 3.20 to 3.21

Bumps alpine from 3.20 to 3.21.

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

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

Author: dependabot[bot]

Dockerfile.signimage

@@ -1,8 +1,8 @@
-FROM alpine:3.20 as ksource
+FROM alpine:3.21 as ksource
 
 RUN ["apk", "add", "linux-virt-dev"]
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 COPY --from=ksource /usr/src/linux-headers-*-virt/scripts/sign-file /usr/local/bin/sign-file
 

Dockerfile.worker

@@ -28,7 +28,7 @@ COPY .git .git
 # Build
 RUN ["make", "worker"]
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 RUN ["apk", "add", "ca-certificates", "kmod"]