feat(ci): use feature branch if specified [php@milan.garnier/publish-ci-builds]

[MilanGarnier]

Motivation

Currently, system-tests run on the latest stable version of dd-trace-php. If a feature branch is specified in the PR title it is silently discarded. This PRs fetches the appropriate build on github's container registry.
In dd-trace-php, a new job publishes builds to the registry, with :branchname. (DataDog/dd-trace-php#4013)

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/scripts/load-binary.sh                                            @DataDog/system-tests-core

[datadog-datadog-prod-us1-2]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 0f0b363 | Docs | Datadog PR Page | Give us feedback!}