Bump alpine from 3.19 to 3.21 in the docker group across 1 directory

Bumps the docker group with 1 update in the / directory: alpine.


Updates `alpine` from 3.19 to 3.21

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

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

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.19
+FROM alpine:3.21
 
 RUN apk --no-cache add \
     bash \