Bump alpine from 3.15.0 to 3.19.1 in /docker/staging

Bumps alpine from 3.15.0 to 3.19.1.

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

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

docker/staging/Dockerfile

@@ -29,7 +29,7 @@ RUN --mount=type=cache,target=/github.com/traPtitech/anke-to/client/node_modules
 
 
 # run
-FROM alpine:3.15.0
+FROM alpine:3.19.1
 WORKDIR /app
 
 RUN apk --update --no-cache add tzdata \