docker: gateway: bump nginx in /gateway

Bumps nginx from 1.25.3-alpine to 1.25.4-alpine.

---
updated-dependencies:
- dependency-name: nginx
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

gateway/Dockerfile

@@ -1,4 +1,4 @@
-FROM nginx:1.25.3-alpine AS base
+FROM nginx:1.25.4-alpine AS base
 
 RUN ["rm", "/etc/nginx/conf.d/default.conf"]