Bump debian from 11-slim to 12-slim in /build

Bumps debian from 11-slim to 12-slim.

---
updated-dependencies:
- dependency-name: debian
  dependency-type: direct:production
...

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

build/Dockerfile

@@ -58,7 +58,7 @@ RUN --mount=type=bind,from=ghcr.io/nginxinc/alpine-fips:0.1.0-alpine3.17,target=
 
 
 ############################################# Base image for Debian with NGINX Plus #############################################
-FROM debian:11-slim AS debian-plus
+FROM debian:12-slim AS debian-plus
 ARG IC_VERSION
 ARG NGINX_PLUS_VERSION
 ARG BUILD_OS