Make the get-latest-components workflow conditional and authenticated

[kishansinghifs1]

Fix #682

1. Add token: ${{ secrets.GITHUB_TOKEN }} to all nmbgeek/github-action-get-latest-commit steps to prevent GitHub API rate limit failures on shared runner IPs.
2. Gate the gather-refs job in system-tests-pr.yml with the trigger-system-tests label check so the workflow skips entirely for unlabeled PRs.
3. Both system-tests-latest-components.yml and system-tests-pr.yml are updated.

Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[precice-bot]

This pull request has been mentioned on preCICE Forum on Discourse. There might be relevant details there:

https://precice.discourse.group/t/gsoc-2026-kishan-singh-system-tests-improvements/2775/1

[MakisH]

Thank you for the contribution.

The conditional check already worked in this PR.

I am not sure if passing the GITHUB_TOKEN would be the right approach here. In #682, the suggestion was for an app id, which we would need to set up.

Let's split this into two. Please remove the authentication aspects, and we see if that's enough. I think it will be.

Btw, I renamed the PR, please rename again after removing the authentication aspects.

[kishansinghifs1]

Hiii @MakisH I was initially thinking of the same but now as you clarified it would be more helpful to me.I'll apply those changes and let you know soon. Thanks for the review!!!!!!!!