chore(deps): bump nginxinc/nginx-unprivileged (#19)

Bumps nginxinc/nginx-unprivileged from `054e14f` to `a8d5564`.

---
updated-dependencies:
- dependency-name: nginxinc/nginx-unprivileged
  dependency-version: alpine
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Dockerfile

@@ -3,7 +3,7 @@
 # The build step (preview-image.yml) runs `hugo` before `docker build`, producing ./public.
 # Pinned by digest so Dependabot proposes (and the routing test gates) base
 # image bumps; the :alpine tag is kept for readability.
-FROM nginxinc/nginx-unprivileged:alpine@sha256:054e14f543eb688809d59ec2ad1644d1a61678e247c87a318ad605977eb37eaf
+FROM nginxinc/nginx-unprivileged:alpine@sha256:a8d5564c3354241473c1e152d5dd3281ab4224edb61b23c291e0bfd9854687a1
 # Serve Hugo's pretty URLs for both /path and /path/ as a direct 200 (no
 # redirect), so the container's internal :8080 never leaks into a Location
 # header behind the preview reverse proxy. See nginx/default.conf.