Compute ref action ref

[rochdev]

Motivation

When using a specific ref of the workflow with uses: DataDog/system-tests/.github/workflows/system-tests.yml@someref it otherwise still uses main for sub-workflows which makes the workflow unstable unless the ref option is set to the exact same ref. This PR basically removes the need for the ref option by detecting and using the correct ref from the workflow call.

Changes

Use current action ref instead of main as default computed ref.

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

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

🛟 #apm-shared-testing 🛟

Reviewer checklist

• [ ] If PR title starts with [<language>], double-check that only <language> is impacted by the change
• [ ] No system-tests internal is modified. Otherwise, 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 (or removed)?
  • [ ] Get a review from R&P team