deps(docker): Bump alpine from 3.20 to 3.21 (#2278)

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

Author: dependabot[bot]

Dockerfile

@@ -38,7 +38,7 @@ COPY --from=build /bin/gomplate_${TARGETOS}-${TARGETARCH}${TARGETVARIANT} /gompl
 
 ENTRYPOINT [ "/gomplate" ]
 
-FROM alpine:3.20 AS gomplate-alpine
+FROM alpine:3.21 AS gomplate-alpine
 
 ARG VCS_REF
 ARG TARGETOS