Bump alpine from 3.20.2 to 3.21.0

Bumps alpine from 3.20.2 to 3.21.0.

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

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

Dockerfile

@@ -24,7 +24,7 @@ COPY . .
 RUN GOOS=$TARGETOS GOARCH=$TARGETARCH go build -ldflags="-w -s" -o /opt/nuts/nuts-pxp
 
 # alpine
-FROM alpine:3.20.2
+FROM alpine:3.21.0
 RUN apk update \
   && apk add --no-cache \
              tzdata \