White-label: core skip link anchor #wp--skip-link--target

Imported from GitHub issue El-SaMa/lamoi-waas#27 by @El-SaMa.

Block themes print a skip link to #wp--skip-link--target (seen on https://arx-e2e-test.intowp.lanetti.fi/ 2026-10-14). Rename the anchor and id in lamoi-brand (filter the skip link output or dequeue wp-block-template-skip-link and print our own), then add it to infra/checks/fingerprint.sh.