chore(deps): Bump alpine from 3.23.0 to 3.23.4 in /build

Bumps alpine from 3.23.0 to 3.23.4.

---
updated-dependencies:
- dependency-name: alpine
  dependency-version: 3.23.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

build/Dockerfile

@@ -2,7 +2,7 @@
 
 ARG BINARY=flipt
 
-FROM alpine:3.23.0
+FROM alpine:3.23.4
 
 LABEL maintainer="dev@flipt.io"
 LABEL org.opencontainers.image.name="flipt"