Update nginx Docker tag to v1.28

Author: renovate[bot]

Dockerfile

@@ -12,7 +12,7 @@ COPY . .
 RUN mkdocs build
 
 # serve the docs via nginx
-FROM nginx:1.27@sha256:5ed8fcc66f4ed123c1b2560ed708dc148755b6e4cbd8b943fab094f2c6bfa91e
+FROM nginx:1.28@sha256:9334faa48d730571746a7baab46d62896cb685502bc29d270c4495e26fc78afd
 COPY --from=0 /docs/site /usr/share/nginx/html
 RUN echo 'real_ip_header X-Forwarded-For;' > /etc/nginx/conf.d/real-ip.conf \
   && echo 'set_real_ip_from 169.254.1.1/32;' >> /etc/nginx/conf.d/real-ip.conf