Bump nginx from 1.29-alpine to 1.31.1-alpine in /container-example

Bumps nginx from 1.29-alpine to 1.31.1-alpine.

---
updated-dependencies:
- dependency-name: nginx
  dependency-version: 1.31.1-alpine
  dependency-type: direct:production
...

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

Author: dependabot[bot]

container-example/Dockerfile

@@ -1,4 +1,4 @@
-FROM nginx:1.29-alpine
+FROM nginx:1.31.1-alpine
 EXPOSE 80
 HEALTHCHECK --interval=30s --timeout=3s CMD wget -qO- http://localhost/ || exit 1
 COPY src/. /usr/share/nginx/html/