Disable automatic ALCF CI runs

[maleadt]

Every Aurora pipeline since 2026-10-10 has failed, on main as well, with ZE_RESULT_ERROR_MODULE_BUILD_FAILURE across most testsets, so the LTS check is red on every PR without saying anything about the change (see also the note on #662 about waiting for the ALCF CI to come back online).

This stops starting pipelines automatically on both ends:

• .github/workflows/alcf.yml no longer runs on push to main or on pull_request. The alcf-ci label still works, now for same-repo PRs too, as a manual way to run it.
• .gitlab-ci.yml drops push from the workflow rules, so the mirror's scheduled sync no longer starts pipelines on Aurora (which alcf-report.yml would otherwise keep reporting as red commit statuses). Pipelines can still be started from the GitLab UI, the API, or the label.

To re-enable, restore the triggers, the fork-only label condition, and the push rule; the header of alcf.yml says the same.

[maleadt]

Turns out the pipeline isn't actually broken, testing is, and you have to check the published logs in a subsequent step.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.58%. Comparing base (fa0f23a) to head (b8ed564).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #688      +/-   ##
==========================================
- Coverage   81.17%   79.58%   -1.59%     
==========================================
  Files          52       51       -1     
  Lines        4085     3953     -132     
==========================================
- Hits         3316     3146     -170     
- Misses        769      807      +38     

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