Bump alpine from 3.20 to 3.21 (#145)

Bumps alpine from 3.20 to 3.21.

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

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

Author: dependabot[bot]

Dockerfile

@@ -49,7 +49,7 @@ LABEL org.opencontainers.image.revision=$VCS_REF \
 
 ENTRYPOINT [ "/which" ]
 
-FROM alpine:3.20 AS alpine
+FROM alpine:3.21 AS alpine
 
 ARG OS=linux
 ARG ARCH=amd64