Bump alpine from 3.18 to 3.19 in /build (#1414)

Bumps alpine from 3.18 to 3.19.

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

build/Dockerfile.nginxplus

@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1.4
-FROM alpine:3.18
+FROM alpine:3.19
 
 ARG NGINX_PLUS_VERSION=R30
 ARG NJS_DIR