Bump alpine from 3.20 to 3.21 in the docker group

Bumps the docker group with 1 update: alpine.


Updates `alpine` from 3.20 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

@@ -27,7 +27,7 @@ COPY controllers/ controllers/
 ENV CGO_ENABLED=0
 RUN xx-go build -a -o source-watcher main.go
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 RUN apk add --no-cache ca-certificates tini