Update Nginx version to latest, 1.29.7

[xlamorlette-datadog]

Motivation

Following delivery of Datadog Nginx module v1.14.0, which notably adds support to Nginx 1.29.7, update the Nginx version in System Tests to this latest Nginx version.

This PR works with DataDog/nginx-datadog#341.

Changes

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

utils/build/docker/cpp_nginx/nginx.Dockerfile                           @DataDog/system-tests-core