chore(deps): bump nginx from 1.28-alpine to 1.31-alpine

Bumps nginx from 1.28-alpine to 1.31-alpine.

---
updated-dependencies:
- dependency-name: nginx
  dependency-version: 1.31-alpine
  dependency-type: direct:production
...

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

docker-compose.prod.yml

@@ -44,7 +44,7 @@ services:
     ports: !reset null
 
   proxy:
-    image: nginx:1.28-alpine
+    image: nginx:1.31-alpine
     depends_on:
       backend:
         condition: service_healthy