Bump alpine from 3.20.3 to 3.21.0 in /dco2-server in the docker group

Bumps the docker group in /dco2-server with 1 update: alpine.


Updates `alpine` from 3.20.3 to 3.21.0

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

dco2-server/Dockerfile

@@ -10,7 +10,7 @@ WORKDIR /dco2/dco2-server
 RUN cargo build --release
 
 # Final stage
-FROM alpine:3.20.3
+FROM alpine:3.21.0
 RUN apk --no-cache add ca-certificates && addgroup -S dco2 && adduser -S dco2 -G dco2
 USER dco2
 WORKDIR /home/dco2