CI: /trigger-e2e-full runs full e2e against latest main instead of PR head

[mamy-CS]

When someone comments /trigger-e2e-full on a PR, the full e2e suite runs against the latest commit on main, not the PR’s head commit.

Cause
The workflow is triggered by issue_comment. In that case, the run is associated with the repository’s default branch (main), not the PR branch.
The e2e-tests job does a plain checkout with no ref:

• name: Checkout source uses: actions/checkout@v4
  So it checks out whatever ref the run is using (main), not the PR head.
  The check-code-changes job correctly checks out the PR head via steps.pr-info.outputs.pr_head_sha, but that ref is never passed to e2e-tests, so e2e still runs on main.
• Failures or passes may be misleading because the code under test is not the PR branch.

Expected behavior
Commenting /trigger-e2e-full on a PR should run the full e2e suite on that PR’s head commit.