Bump alpine from 3.17 to 3.18 in /build

Bumps alpine from 3.17 to 3.18.

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

build/Dockerfile

@@ -36,7 +36,7 @@ RUN --mount=type=bind,from=alpine-opentracing-lib,target=/tmp/ot/ \
 
 
 ############################################# Base image for Alpine with NGINX Plus #############################################
-FROM alpine:3.17 as alpine-plus
+FROM alpine:3.18 as alpine-plus
 ARG NGINX_PLUS_VERSION
 
 RUN --mount=type=secret,id=nginx-repo.crt,dst=/etc/apk/cert.pem,mode=0644 \