update nginx to 1.31.6 to fix libc security vulnerability

[blueelvis]

⚠️ Pre Checklist

Please complete ALL items in this checklist, and remove before submitting

• I have read through the Contributing Documentation.
• I have added relevant tests.
• I have added relevant documentation.
• I will add labels to the PR, such as pr-type/bug-fix, pr-type/feature-development, etc.

Summary

Update to the latest nginx-unprivileged image to resolve the following -

• libc6 -- Installed (2.41-12) -- Fixed in (2.41-12+deb13u4) -- CVE (CVE-2026-0915)
• libc-bin -- Installed (2.41-12) -- Fixed in (2.41-12+deb13u4) -- CVE (CVE-2026-4046)

I have verified and the latest 1.31.6 image has the fixed version.

[klesh]

LGTM