docker-rotate-sa(deps): bump alpine (#12431)

Bumps alpine from 3.20.3 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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

cmd/cloud-run/rotate-service-account/Dockerfile

@@ -5,7 +5,7 @@ COPY . .
 
 RUN  CGO_ENABLED=0 go build -o /rotateserviceaccount -ldflags="-s -w" ./cmd/cloud-run/rotate-service-account
 
-FROM alpine:3.20.3
+FROM alpine:3.21.0
 
 COPY --from=builder /rotateserviceaccount /rotateserviceaccount
 RUN apk add --no-cache ca-certificates && \